Whew, glad I decided to scroll HN right now. I've been puzzling over why I'm getting "! [remote rejected] master -> master (Internal Server Error)" as well while trying to push and decided to take a break.
Guess it's time to go play some video games....
$ while ! git push my; do sleep 1; done
Works for me eventually, although commits do not appear in web interface (they do in the actual repository).