I have quite a few times of late Graham4405 it just cuts your session short or something. But I have only ever had to re log in once and it would be alright last night like I said it took three separate logins to simply continue. It logs you in, in the first place though but then you decide to go to some topic or section so you click on it and then you wonder why you were logged out, and none of the notification's is showing up, no warning not even an error page, it just logs you out. last night was the worst I have encountered it though.
Once you are logged in you should stay logged in till you yourself log out, not have the server making you jump hoops almost. It is only a slight glitch though but to those it happens to it is starting to peeve them off me included.
Other times though like just now you log in and it works perfectly.