I have a Sony Experia Z5 and since the android 6.0.1 upgrade I have had problems with Wifi......Issues 1) Wifi sticking at turning on Wifi. 2) not finding Wifi Networks 3) rebooting when moving between networks.
After playing around for a few months I think I have a solution although only until Sony fix the issue. I believe the issues arise in the way the phone aggressivly hunts for 5 Ghz networks and tries to connect to these first even before SSID appears on the screen. (this could account for battery issues too)
There is no way to turn off the 5GHZ network on the phone. Unless you know differently
So If you have access to the router turn off your 5 Ghz network. If you have connected to 5G networks in the past then make sure the passwords are forgotten to ensure the phone never tries to reconnect to them.(this can be tricky as the SSID will only appear if a 5ghz is on and the phone is liable to hang in the process)
Thats how I have sorted my phone.....A backwards step I know.....Hope it helps you..
