From what I understand, it'll ask a new login if the servers crash between usage sessions of the app. I've not had to log in today, for example, but yesterday I had to two or so times. The login bug is relatively low-priority to me - all it does is force me to switch to the 2FA app and then untick the music in settings. Compared to other bugs, that's trivial.

I'm still occasionally seeing bugs with gyms - for example, instantly kicking me back to the gym screen as soon as I try to battle - but that's fixable by going and battling another gym. I've yet to see a way to solve the other big gym bug wherein enemies stay at 1hp but never die or do anything until the timer runs out.

Otherwise, the standard client/server sync bugs (pokeballs sitting on screen doing nothing if you lose server connectivity during capturing it) and client-side bugs (battery saver mode cuasing the game to become completely unresponsive to touch sometimes when you bring it back by turning your phone upright again) are the main gripes.