500 when testing drone service integration

On gitlab.com.

For the last few days gitlab has been creating multiple builds for the same commit in my drone CI server. It appears to be posting multiple times to the hook about 50 seconds apart. Going to the services page (services/drone_ci/edit) and clicking 'test' generates a 500 internal server error, I suspect they are related?

From my investigation on the drone side the request looks fine and a 200 response gets sent back after about 4 seconds.