Was playing for about a week solid (after a 6 month+ break) literally up until the Research update came out, when the research update dropped and I installed it I haven’t been able to log into my main since.
However, I can log into all my side accounts.
Factory resetting my phone,
Reinstalling Pokemon GO,
Clearing my Google account from all devices,
Changing my password,
Clearing Cache, clearing Data,
Logging in on different (four total) phones,
and I’m sure I’m forgetting some other things I’ve tried.