Error: Invalid solution received for slot 859751: SectorExpired { expiration_history_size: HistorySize(7), current_history_size: HistorySize(10) }

This might happen in case replotting isn’t quite able to catch up, in that case you’ll see some sectors expiring before they are replaced with an updated version and when node receives corresponding solutions it’ll ignore them.

If this is happening rarely, then I wouldn’t worry too much. Also this will happen less and less frequently over time, see What triggers a sector to start replotting for details