Error 500 on mirrored repo

Hi, I’m getting an error 500 when I open a mirrored repository, the log shows GetBranches: No branches in non-empty repository after the attempt.
Trying to clone returns an empty repository, yet it uses ~100MB on disk. Is it possible to recover it?

After cloning, are any branches listed when running git branch -a?

If not, my guess is mirror repository is corrupted somehow. If you get significant errors when running git fsck --full, you could try a tool like git-repair to see if it is salvageable.