After SPM-3489, we will now send an updatePosition command after advancing lastWritten, lastApplied, or lastDurable. If our upstream node receives the lastWritten updatePosition before we have managed to update lastApplied, the upstream node will see the lastApplied value as out of date. Since lastApplied is used to calculate lag in FTDC, this can lead to a confusing report of temporary lastApplied lag when there is very little lag to begin with.

This is more evident in scenarios where writes are infrequent for the set, since the node's lastApplied corresponds to the previous applied oplog entry batch. If the last batch was applied 15s ago, then the lastApplied lag is reported as 15s for a short period of time, before quickly dropping back to 0.