Endless "Please Log in" loop

Every time I try to log in to my account, it takes me back to the login screen. For months now the app has been slowing down, not loading etc. I uninstalled it just for it to log me out and now, despite me using two different phones I am stuck in an endless loop of putting in my login, verification, right back to the login screen. I've used wifi, phone data and two phones and it keeps happening. What am I supposed to do, exactly?