Use last optimistic status on batches (#12741)

* Use last optimistic status on batches

* more descriptive errors

---------

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

beacon-chain/blockchain/receive_block.go

@@ -185,16 +185,18 @@ func (s *Service) ReceiveBlockBatch(ctx context.Context, blocks []interfaces.Rea
 		return err
 	}
 
+	lastBR := blkRoots[len(blkRoots)-1]
+	optimistic, err := s.cfg.ForkChoiceStore.IsOptimistic(lastBR)
+	if err != nil {
+		lastSlot := blocks[len(blocks)-1].Block().Slot()
+		log.WithError(err).Errorf("Could not check if block is optimistic, Root: %#x, Slot: %d", lastBR, lastSlot)
+		optimistic = true
+	}
 	for i, b := range blocks {
 		blockCopy, err := b.Copy()
 		if err != nil {
 			return err
 		}
-		optimistic, err := s.cfg.ForkChoiceStore.IsOptimistic(blkRoots[i])
-		if err != nil {
-			log.WithError(err).Debug("Could not check if block is optimistic")
-			optimistic = true
-		}
 		// Send notification of the processed block to the state feed.
 		s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
 			Type: statefeed.BlockProcessed,