500 error requesting commit for ref

Requests for a single commit via the api on are failing with 500: Internal server error

Following the docs at we are making a request to e.g.

This is currently returning {"message":"500 Internal Server Error"} instead of the expected reply that worked until very recently. We noticed failures starting some time yesterday, but it could have started earlier. This seems to fail for all projects we can find. For the same projects, ../commits?ref_name=master works fine.