500 Errors in /api/v4/projects/<project_id>/repository/branches/master

https://log.gitlab.net/goto/d0e571f3c5370e337c5af610f774e399 shows a steady stream of 500 errors:

The quick Kibana summary shows that of 500 entries, 30% of them belong to:

/api/v4/projects/4655045/repository/branches/master

That endpoint works fine for me as an admin user. I can't seem to get it to return a 500 error.

The reason I'm interested is that I've been seeing unusually high call times from the handle_api_exception method in there and in the commonly called /api/v4/internal/allowed endpoint:

This method logs an error to Sentry, but I can't seem to find relevant Sentry errors. I'm wondering if Sentry queuing is delaying the return of this method.