Let's please not be so quick to dimiss people with issues just because you aren't having the same problem. They obviously had a working network before, and now they do not after the update. Saying things like "Nah mine is working fine so it must be your ISP" is not helpful. I for one have had nothing but problems with the 8.1 update on my HTC 8XT. Including but not limited to: Wiped carrier settings, wi-fi radio crashing when the phone goes to sleep, which require a restart to fix, and constant reboots both during use and while the phone is asleep, inability to read SD card, phone won't wake up from sleep, and those are just the problems that make the device non-functioning, let alone the bugs that reduce it's usefulness and the crippling of old features (music and photo hubs)
The problem with wifi seems to be for most people that the radio crashes when the phone goes to sleep, and won't work again until you restart the phone (if it doesnt restart by itself first) You can try to set wifi to only be enabled manually. This is what I'm trying next and I know it is going to be very cumbersome. If you have not hard reset yet, I would recommend giving it a try with your fingers crossed, and do not restore from a back up. Start with fresh settings on your phone.
I understand this was a developer "preview" but being an official update available from Microsoft, I did not hesitate as much as I should have when trying this update. My phone is essentially a paperweight now. I'm just glad I got cell working again so I can text my wife and babysitter.
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