I use a Samsung Galaxy S5 with Resurrection Remix Rom (Nightly with Marshmallow) and WhatsApp 2.12.479.
Starting the "normal" camera and using it is no problem. It works fine.
All I could find with google are problems regarding a flipped scanner, but as you can see that is not my problem :/.
I already reinstalled WhatsAPP, but it doesn't work.
Thanks for your help,