Periodically (every few minutes) the credential manager for Bitbucket/Atlassian shows up when I am running Sourcetree. I can cancel the popup window and go to my authentication options in Sourcetree. I have three accounts connected: two GitHub and one Bitbucket. I use OAuth on all three accounts, but it seems the authentication for Bitbucket expires and I must go through the process of refreshing the token. Neither GitHub authentication tokens expire.
I can refresh my Bitbucket account without any issues, but then it will expire and I will get the credential manager popup within minutes.