Hi,
what I tried some days ago was the following:
- Turn phone off and wait about 1 minute until it is completely down.
- Turn phone on again and wait until it is fully started.
- Go to "Settings" and turn Bluetooth on. Wait about 1 minute.
- Turn Bluetooth off again and leave it turned off.
After that, WiFi on my phone was stable for almost exactly 106 hours, then WiFi turned off again, and I had to restart the phone.
It seems, though, that the WiFi connection is more stable with Bluetooth turned off.
An expert just told me that obviously a firmware update is needed to fix the problem, as Bluetooth and WiFi use the same frequencies. The recent firmware update to 01078.00037.16082.41014 on my Lumia 650 definitely did NOT fix the problem or lead to any improvements.