I can give some of my own experiences. I am using chrome.
Just lately I have also had issues where I will log in, and i see that i HAVE been logged, but then i may go to the forum and click general to see that i am now NOT logged in. To post it says you need to log in.
But i can then click on another tab like "blog"and then i see that i AM logged in, i click on forum and then general and see that I am not logged in.
So I go back to the forum page where i see at the top where i am now not logged in, i then click log in, and I will log in again but just for that page.
But then when i click the home tab i will see i am again not logged in, but it only happens when i click the home tab. It;'s all very funky,