Can't log into the game.

Recently my research tasks have been bugged I.e. a blank white screen appeares when I try to claim a Pokemon reward from them. I unwisely tried to reinstall the game 12 hours ago to fix it, since then I am completely unable to log in from my phone, I get this error message (though I can log in off someone else's.)

Anyone know why, please? Before anyone offers the usual cliche replies;

-reinstalling the game does not work (has reinstalling the game ever actually worked for any bug?)
-I have Never spoofed, nor attempted to. I also do not have any IV calculators, Pokemon trackers etc on my phone. So I assume I haven't been banned.
-Turning WiFi on or off makes no difference.
-My internet works normally elsewhere.
-Other people can still play, so it's not the Niantic servers. I've never received this particular error message before.
-4G is turned on.
-I have not emailed Niantic, I think that would be a waste of time.

I deduced it's a problem with my phone but don't know what. My phone is an Android.