I encountered this problem and found the real trigger process,
The details are:
When calling the Web login page, FireBase should open an activity,
After the FireBase activity is enabled and before the web page is opened, if you go back,
This will cause FireBase's activities to fail to listen to the Web's exit monitoring,
As a result, FireBase's logic can't handle the listening logic after the Web page exits, and it is always logged in
The details are:
Originally posted by @yangnnytao in https://github.com/firebase/quickstart-unity/issues/1267#issuecomment-1311185986