Have you tried backfilling again since the last RPC error? If you have tried, was it still giving the same error or did the backfilling complete? You might want to try it out on one calculation first instead of doing it all in a bulk.
The [-10727] error is usually related to connection/communication issues between the applications or subsystems. Since you mentioned that there were outage and system shutdown, it might be good to check on the health of the affected systems especially if the PI Data Archive was shutdown. Older versions of the PI Data Archive are more prone to corruptions due to ungraceful shutdowns.
For more information about this error, you can review KB01668.