Just a quick sanity check since no one mentioned this yet: any chance that you have enabled the Master Password Reprompt feature for the items you are trying to autofill?
If not, I would suggest filing a bug report (“New Issue”) on Github (after checking whether you can find an existing issue that describes the same problem). At the very least, this will get you a determination as to whether Bitwarden considers the behavior to be a bug or “intended”.
I also found an old thread on the forum, which I haven’t read through myself, but which may contain some information relevant to you: