My main problem with passwords is the limits that sites put on what I can set for a password.
I could not tell you how many times I reset my password using my password manager, then immediately log out, and log in using the credentials I just saved into my password manager, and they don't work, because the site is truncating the password to 15/20/whatever characters.
The number of times this limitation is not clearly stated, checked for, or even acknowledged by the site is too damn high.
I've made it a habit of testing a login after every password set/reset to ensure I don't have trouble with it in the future.