When processing a thumbnail retrieval job, the Unity Scheduler waits up to 100 seconds for a response from NilRead. If there is no response, the job times out with an error.
If a thumbnail job errors out, the job is eligible to be retried after five minutes. Once eligible, the job is retried after the Unity Scheduler finishes processing all other thumbnail retrieval jobs in the queue.
Thumbnail jobs that error out are deleted after six months if they are still in an error state.