We acquired two Xperia M5 phones on 09/04/16 and are experiencing the same problem with both. We are having to log in to our home (Virgin) wifi everytime we wish to use it. Even if the phone 'sleeps' connectivity is lost.
When out and about the units will connect to various wifi networks but, again, loses connectivity upon sleeping.
Hi Mat, it is a Super Hub 2. We are also having problems with the wifi on the local bus service and at our local pub ( catastrophe - we may have to talk to one another!).
I did not manage to connect on the bus, a feat that never failed with my old Moto G, and had to 'forget' and reconnect with the pub. Teething troubles I am sure but any help would be gratefully received.