When you leave your tabs open, as many people do, your session can expire, that’s fine.
What is really annoying is that you are able to start adding a new password on an expired session. So you are able to click add new password, and fill in the fields, generate a password, and then when you are all ready to save all your info (even when you entered the generated password to the website you just registered to) then it tells you your session is expired.
Could you add a check if the session is active when opening the screen to add a new password? That would solve this annoying situation