To reproduce:

• Run a sharded cluster on 2.2 that contains at least one collection created in 2.0.
• Start up a mongos with the --upgrade flag to start the process of converting chunks metadata to have the "lastModEpoch" field
• After mongos is up and running:

  { "_id": 1, "version": 3, "minCompatibleVersion": 3, "currentVersion": 4, "clusterId": ObjectId("511eb84c6e9141cef5f7a0ab"), "upgradeId": ObjectId("000000000000000000000000"), "upgradeState": { } } 
  

The upgradeId and upgradeState fields are still there.