I'm adding this so it will be searchable for anyone else who runs up against the issue of a scheduled dashboard not sending ***WITH NO WARNING OR ERROR**** while other scheduled dashboards continue to run quite nicely.
Answer in first comment so I can mark this solved.
Solved! Go to Solution.
Apparently there is 1) a limit of 50 recipients for a dashboard and 2) that limit includes addresses in a group so if you have 30 recipients and one group of 30 that dashboard isn't going anywhere and - alarmingly - there won't be any indication that it has not ( and therefore *why* not ) until the phone rings and it's a customer asking where their dashboard is.