Hey,
Sounds very much like what happened to my device - also a 6. No problems for a couple of years, until suddenly it couldn't maintain any wifi connection. Even when I sat next to hub, signal weak. GPS also deserted me, no tracking journeys or pinpointing current location. I took all the steps you've mentioned: Network settings reset, data removal, until finally I accepted my fate. Deleted & Reset to factory settings. Begrudgingly I acknowledged if it had to be done to sort the prob, so be it. Restarted phone. Restored etc. Connected to WiFi and....same sodding fault.
Apple Support weren't able to tell me exactly what, or why, this happened. But advised me it that I had an issue with the hardware - mercifully all of my data I'd backed up was fault free - I checked to be sure by wiping the handset again, and this time not restoring but rebooting as new device. Connected to WiFi...and yup no cigar. Knew I was out of warranty, Apple confirmed replacement would be needed.
Claimed on my insurance, have another 6. Financial cost the excess, and all the bloody data bolt ons I'd been forced to add. But it was my soul that paid a higher price; The constant, burning rage. The frustration. The bitter despair and self pity. The harsh reminder of the unfairness of life. Plus some messages, pics etc that can't be retrieved.
Wish this wasn't bad news - or that your issue is different. Either way, you have my sym
