Password manager does not keep password on file at times.
I have 4 email accounts on Thunderbird. Upon opening Thunderbird, at times, the password manager responds that the password has to be r-entered. I have to re-input the password for that email account, sometimes often. The password manager does not hold this information regardless that I check the box for "password Manager" to remember password.
ప్రత్యుత్తరాలన్నీ (1)
If your connection is unreliable, Thunderbird may attempt to login and fail. It may assume that the failure is due to an invalid password, and so asks you to re-enter it.
Does it actually store the password? You can check here: Tools|Options|Security|Passwords→Saved Passwords