I have experienced the same issue for over two weeks now and I no longer want to use ebay. In fact, I lost an item because ebay made me sign in after I bid on an item and before I could confirm my bid.
I just completed two sessions (wasting over thirty minutes) with ebay live reps. The first one told me to clear my internet history and that would resolve the problem. It did not. The second session got me to ebay security - who told me that for security reasons, ebay was making everyone sign in more often. And, that there was nothing I or anyone else could do to fix the problem - constantly having to sign in when you tried to change pages.
I think everyone who has this issue should stop using ebay until the problem is resolved.
And, don't forget how hard it is to get to ebay customer service to identify your problem. Try the following for a direct link:
Link Good luck!