I've recently started getting these errors when I try to implement a feature through git flow. Pushing & pulling to branches in Sourcetree work correctly so I'm certain it's not an issue with my account setup.
I've tried changing my account connection from basic to oAuth and I still get the same error when I try to complete a feature through git flow.
I'm running Sourcetree 3.0.1 on High Sierra 10.13.6. Has anyone else experience this and managed to solve it?