I had one weird login where the limitations were done on the input field (but not enforced on the backend), so if I typed my password in, it didn't work, but if it autofilled with a password manager, it did work.
I had the opposite happen to me. The password length was enforced on the frontend by JavaScript, which the password manager bypassed. The backend recieved the whole string though, so I could only log in by pasting in the password, which got truncated by the client side JavaScript. Drove me nuts until I figured it out.
