WiFi disconnects in sleep mode after software update

[dumbanddashing]

I have recently updated my software on my Sony Xperia E5 (and it's been a disaster). Since the update the phone automatically disconnects from the WiFi as soon as it goes to sleep mode. I have tried Always On during sleep, network settings reset and everything that I could find on the Internet regarding this issue but in vain ..

I even factory reset my phone twice but soon after the reset it auto updated the software and boom , I am back to square one... 

Any genius mind knows the solution or another factory reset z doomed ? 

[Uliwooly]

@dumbanddashing

Do you have STAMINA mode on?

[dumbanddashing]

Stamina mode z OFF