I had CyanogenMod 12.1 on my Nexus 4 and after switching to the Sony Xperia Z3 I installed the newest nightly, too. On both phones I have trouble getting WhatsApp Web to work.
I can scan the QR code without problems but ~50 % of time the loading spinner on the website won't disappear. Removing the browsers in the app doesn't help and even removing the app's data and setting it up from scratch didn't change anything.
I have the same problems using 3G or WiFi and also in different WiFi networks (home/work).
Sometimes, the following exception appears in the LogCat
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.030 14060-14097/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.055 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.056 14060-14091/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.058 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.059 14060-14100/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.060 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.061 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: Caused by: java.lang.Exception: delivery failed
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.a(m.java:2)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at org.whispersystems.jobqueue.m.run(m.java:4)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: java.util.concurrent.ExecutionException: java.lang.Exception: delivery failed
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.a(bh.java:17)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.messaging.bh.get(bh.java:16)
10-09 14:32:11.062 14060-14101/com.whatsapp W/m: at com.whatsapp.jobqueue.job.b.k(b.java:1) enter preformatted text here
