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.