On a near daily basis, Bitbucket will stop working when trying to do things such as going to a new page, uploading an image in a comment, trying to tag someone in a comment, etc. It'll usually report something generic such as "something has gone wrong". If I refresh the page via F5, it redirects me to https://bitbucket.org/socialauth/login/atlassianid/?next=... which appears to log me in or refresh my session, and then I get redirected back to the page I was on, and then everything starts working.
I'm not sure how long Bitbucket sessions last, but it appears the session times out after XX hours even if I'm actively using Bitbucket. It would be much better if the session automatically was extended which would avoid sessions expiring minutes after interacting with Bitbucket and Bitbucket suddenly stop functioning normally with "something has gone wrong" messages requiring a full page refresh to get a new session and losing unsaved changes.