[BP 7.2] Index build can hang in mixed mode due to projector skipping transaction records

        isTxn := (m.Opcode == mcd.DCP_MUTATION) && !m.IsJSON() && m.HasXATTR() && bytes.HasPrefix(m.Key, transactionMutationPrefix)

        if isTxn {

            worker.stats.txnSystemMut.Add(1)

        }

        // If the mutation belongs to a collection other than the

        // ones that are being processed at worker, send UpdateSeqno

        // message to indexer

        // The else case should get executed only incase of MAINT_STREAM

        // (or) when a transactional mutation is being processed in

        // INIT_STREAM

        if collEngines, ok := allEngines[m.CollectionID]; ok && !isTxn {

            processMutation(collEngines)

        } else {

            // Generate updateSeqno message and propagate it to indexer

            worker.stats.updateSeqno.Add(1)

            if data := v.makeUpdateSeqnoData(m, allEngines); data != nil {

                worker.broadcast2Endpoints(data, worker.runFinCh)

            } else {

                fmsg := "%v ##%x SYSTEM_EVENT: %v NOT PUBLISHED for vbucket %v\n"

                logging.Errorf(fmsg, logPrefix, m.Opaque, m, vbno)

            }

        }