Heavily using the github api quota seems to lock executors for a period of time. They are not zombie jobs as they eventually clear out but it takes a while. The jobs themselves run fine when our quota usage is low.
The jobs in the attached screenshot all finished successfully but the executor refuses to unlock for an hour or so afterwards.
I thought that it might be just hanging waiting for the quota to refresh but even after refresh they stay locked with the logs stating that the build has finished.