https://github.com/mongodb/mongo/blob/aaac2c39a7f8066ea8cffb9a86fed595704a3b2d/src/mongo/db/repl/replication_recovery.cpp#L161
In this log line we log "numOpsApplied" before it is incremented by the upcoming batch size. I think this might be because we haven't yet applied these ops yet so we don't want to preemptively log it but since the subsequent log line about actually applying individual ops is not always logged, if there's only one batch we end up not knowing how many ops will be applied.
It would be helpful if we changed this log line to log the number of ops that will be applied.