Mongos can return the wrong topologyVersion in state change error responses to the client. Instead of returning its own topologyVersion, mongos can return the topologyVersion of a shard member in some error responses.

I've attach a reproduction script using failCommand (reproMongosWrongTopologyVersion.js). It's also possible to trigger the same bug using a real shutdown or replSetStepDown event. To reproduce:

1. Start a cluster. Mine has 1 mongos and a 1 member shard.
2. Note the topologyVersion reported by the mongos.
3. Insert into test.test
4. Run an operation on mongos, my example uses findAndModify but I imagine other commands will also reproduce.
5. At the same time, cause the mongos-mongod operation to fail. This can be done with failCommand, shutdown:1, etc...
6. See the operation fails and mongos returns a error with the incorrect topologyVersion.

The attach repro script's output (notice the different topologyVersion fields both reported by mongos):

mongos topologyVersion:  {
	"processId" : ObjectId("5f501dd34f1464b2cf98116a"),
	"counter" : NumberLong(0)
}

...

uncaught exception: Error: findAndModifyFailed failed: {
	"topologyVersion" : {
		"processId" : ObjectId("5f501dcf33e67a0de9b4ab21"),
		"counter" : NumberLong(8)
	},
	"ok" : 0,
	"errmsg" : "Failing command due to 'failCommand' failpoint",
	"code" : 11602,
	"codeName" : "InterruptedDueToReplStateChange",
	"operationTime" : Timestamp(1599086037, 28),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1599086037, 28),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
DBCollection.prototype.findAndModify@src/mongo/shell/collection.js:730:15
DBCollection.prototype.findOneAndReplace@src/mongo/shell/crud_api.js:833:12
@reproMongosWrongTopologyVersion.js:27:11
failed to load: reproMongosWrongTopologyVersion.js
exiting with code -3

It's possible this could be fixed by SERVER-50549 but I wanted to call out this bug separately.