Tagging and Untagging servers can lead to an unexpected state

**Background:**
I tagged a few servers with a tenant ID (Cell19) but after a while I realized that I had incorrectly tagged some servers as the actual AZ distribution did not match with the expected AZ distribution. So i untagged a few servers but I retagged other servers to have the right AZ distribution.

**Issue:**
This is leading to a state wherein the Helix/Zk thinks that the older servers are still part of the tenant but the server does not have the old tenants tag on it.
The new servers have the tenants tag but theyre not actually ingesting anything.

List of instances on the tenant page

Server that was added later on( this is not doing any work)

Server that was removed from the tenant. As you can see, it does not have the tenant tag (tenant was 'Cell19')

Start by reproducing the reported sequence: tag servers for tenant Cell19, untag some, and retag others with a different AZ distribution. Inspect the tenant page, Helix/ZK state, server tags, and ingestion status to identify why removed servers remain assigned while newly tagged servers do no work; done means tenant membership and ingestion match the current tags.

Written by the indexing model from the issue text.