Login failure: “An error has occurred with the wireless network.”
Like several others who have reported this today, I've had this problem since around 4am (UK time).
Something obviously changed on Niantic's servers at around that time.
(I suspect this is related to a new asset having been introduced into the game, as you'll see below)
I reported the bug to Niantic support, but after over 12 hours I have yet to receive either an acknowledgement or a solution.
A bit disappointing as today is/was Community Day.
However, it looks like I've just managed to fix it myself, but first, here's what didn't work:
Using mobile data instead of wi-fi to login.
Rebooting the phone and then trying to login.
Clearing the cache, rebooting the phone and then trying to login.
Clearing cache and data, rebooting the phone and then trying to login.
Uninstalling the app, rebooting the phone, reinstalling the app and then trying to login.
Logging in with a new account - the new account crashed on logging in, in the same way as my normal account. At least, at first...
And here's what did work:
Uninstalling the app, rebooting the phone, reinstalling the app and then logging with a new account.
There was a long pause whilst the app downloaded various assets, but eventually I was able get as far as the tutorial for new players.
However, logging back out and switching to my normal account brought back the dreaded "An error has occurred with the wireless network."
I then uninstalled and reinstalled the app again, and logged back in using the new account created above - but this time when I got to the tutorial stage I took the option to download all the "essential assets" before logging out and (finally!) logging in successfully using my normal account.
I'll never catch up on all the hours I've lost from today's Community Day, but hopefully this will be useful to anyone else who finds themselves in the same situation.