For the longest time, Lemmy had no feedback loop for accounts which had been rejected, you got an infinite loading screen and that's it. No easy to see explanation for why your login wasn't accepted. If you are denied, now you will finally see the reason why in the login page in the form of an error toast in the bottom left corner. Such as the following example I did on a test account.

If we haven't yet gotten to your application, it will say something along the lines of "could not find account, does not exist" or something like that.