Login issues:
Clear cache/ cookies then restart the browser
Delete old bookmarks that use HTTP:// links. Update them to HTTPS://
Doing the second one is probably enough for most people.
Anytime you get logged out check the URL bar and see if it's HTTP. That means you got there via an old link/bookmark.
It's happening to me as well as I'm often logged out after returning to this forum. Actually the odd thing is, if I actually go click on any thread, I'm mysteriously logged back in!
This means you are getting to HF via a bookmark or your browser history and it's still using the HTTP link.
Clear out your bookmarks and history and update them to HTTPS links.