On step up we both recover pending migrations and resume range deletions. In particular the following interleaving of the two operations could make the recovery to be skip.

• On step up a collection with pending migrations is marked as "needs recovery" by setting its metadata as unknown and a recovery is triggered by an asynchronous call to onShardVersionMismatch.
• On step up in order to resume range deletions we force a metadata refresh for the collection with the result of populating its metadata.
• When onShardVersionMismatch will finally run it fill find that the metadata are known and it won't even try to do a migration recovery.