Crash with authentication in Corporate proxy

I use a corporate proxy to access an internal github where our projects are stored. When I switch to the proxy connection, Sourcetree always crashes within seconds. It constantly asks for my credentials for the proxy but when I enter them (I've confirmed they are correct) it just asks over and over.

This doesn't seem to matter as I can pull and fetch either way, but only if I manage to very quickly perform it as it usually crashes within a few seconds of dismissing this dialog.

The crash log is here:

 https://pastebin.com/t6URPcZ9