The setOrphanCountersOnRangeDeletionTasks work done during upgrade to FCV 6.0 loops through all range deletion tasks and issues an update for each document to add the number of orphan documents to the task.

However, this work is not synchronized with the removal of completed range deletions having their task documents deleted. We do take the ScopedRangeDeleterLock, but this only prevents us from modifying the number of orphans, not actually removing the document.

I would propose that we should simply swallow these errors (note that depending on where we are in the execution of the update, we can either receive WriteConflictException or NoMatchingDocument) because if the task is removed we have no need of the orphan count.