For months I tried to track down a ping issue (high ping; disconnect & reconnect my router; low ping for about 20 minutes; high ping again). Turns out, thanks to this answer, it was the Google+ auto backup feature (that, for some reason, seems to kick in several minutes after it gets a connection).
The Google+ auto backup feature is enabled on my phone. It is configured to upload in "standard size" (not "full size"). Also, it is set to only upload if charging and if on WiFi.
During backup, the ping time (from my laptop, but the same applies from the router's admin page) goes up to over 7000 ms, see:
If I disconnect my phone from WiFi, the ping time goes down to about 50 ms.
What can I do to avoid this from happening? I tried to search for some way to set WiFi bandwidth limits for a specific app, but I couldn't find any.