An unlikely sequence of config server stepdowns and concurrent operations during the execution of the removeShardFromZone command can create an inconsistency by leaving a zone without any shards associated (usually, a ZoneStillInUse error would be thrown).

Reproduction steps:

1. Add a fail point hangRemoveShardFromZoneBeforeCommit in the following line of code.
2. Start a sharded cluster with at least two nodes in the config server replica set and --setParameter enableTestCommands=1.
3. On the mongos router, add a shard to a zone: sh.addShardToZone("shard01", "NYC")
4. On the CSRS primary, enable the fail point: db.adminCommand({configureFailPoint: 'hangRemoveShardFromZoneBeforeCommit', mode: "alwaysOn"})
5. On the mongos router, remove the shard from the zone: sh.removeShardFromZone("shard01", "NYC"). The command will hang.
6. Step down the CSRS primary: rs.stepDown()
7. From the mongos router (on another shell), associate the zone to a key range: sh.updateZoneKeyRange("records.users", { zipcode: "10001" }, { zipcode: "10281" }, "NYC")
8. Step down CSRS primary(es) until the original config server primary gets elected primary again: rs.stepDown()
9. From the CSRS primary, disable the fail point: db.adminCommand({configureFailPoint: 'hangRemoveShardFromZoneBeforeCommit', mode: "off"})

At this point, the hung removeShardFromZone command will complete successfully and the zone will be orphaned.

> db.getSiblingDB("config").tags.find()
{ "_id" : ObjectId("67082f58eee0b05d5418e785"), "ns" : "records.users", "min" : { "zipcode" : "10001" }, "max" : { "zipcode" : "10281" }, "tag" : "NYC" }
> db.getSiblingDB("config").shards.find()
{ "_id" : "shard01", "host" : "shard01/localhost:27018", "state" : 1, "topologyTime" : Timestamp(1728589374, 13), "replSetConfigVersion" : NumberLong(-1), "tags" : [ ] }

A fix possibility is adding a call to opCtx->setAlwaysInterruptAtStepDownOrUp_UNSAFE(); at the beginning of the command.