Why does the vehicles & drivers endpoint return 0 records?

We are periodically syncing the vehicles and drivers from Samsara; the schedule runs every 4 hours.

We have started to notice issues where the endpoint for vehicles & drivers returns http status 200 but with no data. This appears to happen at 04:00 utc (and potentially on Thursdays). Is there a maintenance window that we should be aware of - and if so should the endpoint return a http status code of 503 to indicate that the service is unavailable (perhaps with a message to indicate service will be resumed at a specific time)?