When a new server is started, or after a merge, the other servers may see it as a an owner in the consistent hash before the other servers see its server address in the address cache (___hotRodTopologyCache). When a server needs to send a topology update but some of the servers are missing from the address cache, it can't send the topology update, so it tries to send a "partial update" that excludes the missing servers from the segment owners. In order to send the full topology update when the address cache is populated, the partial topology update has to be sent a smaller topology id, and that means it is only send if serverTopologyId >= clientTopologyId + 2.

When the cluster splits and the cache becomes degraded, the servers in the other partition are removed from the address cache, but the list of segment owners is not updated, and the topology id is only incremented by 1. The address cache is incomplete, but a partial update cannot be sent, so the client keeps the old topology and keeps trying to connect to the servers in the other partition.