From time to time SourceTree asks for Bitbucket password

I enter correct password and everything works fine. But after some time the dialog appears again.

My Tools > Options > Authentication looks like this

If I click on Edit I see the dialog that says Login Failed.

I click Refresh OAuth Token button and the token gets refreshed successfully. But after some time, when Source Tree starts asking for password, I get back to this dialog and it again says that Login failed and I need to refresh the token again. This can happen every 10 minutes or once in 1-2 hrs. Very random.

The problem happens only on one of my computers. I'm using desktop, virtual and laptop. And the problem happens only on my desktop.

I've tried to uninstall and install SourceTree. Nothing helps. Please help with this annoying problem.