A few users reported that sometimes browser's caching may cause logout issues. You can either clean the cache or just do Ctrl+Refresh after you login to force it on that page.

Anyway, I'm glad you got it figured out quickly.
Thank you for your follow up and good luck sniping.

Nevermind, figured it out

And now I can not enter the page at all - it says "Your eBay account is not linked to the sniper." The app works fine at the same time.

I can login just fine, but when I try to go to the last page I get kicked back to the login page. Both IE and Chrome.