the session doesn't cleared until the request gets validated
If that doesn't help, compare the submitted token value with the one currently stored in session. If those two don't match, you most likely have a problem correctly setting cookies or maintaining the session throughout several requests.
Since you also get logged out it seems that the current session actually gets cleared somewhere (which removes both the _token and the current user from the session, resulting in the behavior you described).
Do you have any calls to Session::clear(), Session::forget() or the likes in your application?
Can you do a dd(Session::all()) and check if the contents are as you expect?
Also, it's possible that the permissions on the sessions directory changed after session files were created successfully. Try to delete all files inside sessions (assuming that you're working in a dev environment) and check if a new one is created once you hit the page in question.
If multiple files are created for multiple requests all issued by yourself, this is another indicator that your Session object gets cleared somewhere along the way.