It should be possible to create a Subagent Cluster

 Current Situation

Agent Cluster A1 is assigned Contoller C1
A1 has Directory Agent Primary DP1
A1 has Directory Agent Secondary DS1

Manage Subagent Cluster
Add Subagent Cluster SAC
Drag and Drop DP1 to SAC
Drag and Drop DS1 to SAC for fixed-priority mode

DS1 will be added for round-robin mode.
DS1 cannot be removed
DP1 cannot be removed

Leave the page and then re-enter

Now DS1 can be assigned for fixed-priority mode.
DS1 can be removed
DP1 can be removed

Desired Behavior

Adding a Subagent to a Subagent Cluster and removing Subagents should work directly after creating the Subagent Cluster.