Credentials prompt keeps popping up and disappearing

[Janice Cadel _ Shiji]

I'm successfully logged into SourceTree, but every so often the credentials pop-up window pops up but then disappears. I am able to successfully perform all operations in SourceTree. Is there a reason why this may spontaneously pop up and disappear? Is there anything I can do?

Also, I do not know if this has anything to do with it, but I randomly get this pop-up message: