Everytime I open the app it forces me to log into my account (which has two-factor authentication enabled). Every single time.
My guess is that two-factor auth only gives the app some sort of one-time use token which 'expires' or stops working when I open the app again.
I wouldn't like to turn off the two-factor auth, as I consider it an important security feature for my GMail account.
I've installed the app twice and still face the same issue.
Could it be only happening in my device or is it more of a UX (or software integration) problem here?
If it is a real issue, then it'd represent a dangerous (yet somehow ironically funny) security breach, because a lot of people would be disabling their two-factor authentication just to "catch 'em all!"
Create an app specific password just for the game.
Some very early Ingress players had to do that. No rhyme or reason to why one account will work, others wont.