Something similar happened to me recently. Showed me as logged in, but I wasn't and while I could see eg MY HOME page, noting would open as I wasn't logged in.

Two possible reasons.
1. Shonky cookie on my PC.
2. Interference by a password security program or "app".

Or a combination of both. Closing the browser and reopening, hit refresh a few times etc. Something along these lines helped. Deleting the cookie and getting a new one would probably also work. Flushing out the memory cache might also work at these times.