I still am unable to produce a proper minimal reproduceable example — I've been busy with feature implementation to dig this further, but depending on some context to be determined, in the method_parse_progress_line() of RemoteProgress sometimes the line argument is a bytes string, other times it's an str string.

I've hit the issue with my implementation in guyzmo/git-repo and to fix it I've made the following fix at line 387 of git.util:

self._cur_line = line = line.decode('utf-8') if isinstance(line, bytes) else line

This issue has been noticed with GitPython 2.1.0, I'm upgrading it locally, to see if it hasn't been fixed with 2.1.1, so please pardon me if it's been fixed ☺