Quick answer: Unreal Control Rig stops driving bones after the underlying skeleton's hierarchy changes? Rig bindings store bone indices, not names - re-bind in the rig editor or use Bone Reference by Name.
Renamed a bone in the skeletal mesh. The Control Rig that drove it now does nothing.
Re-bind in rig editor
Open the Control Rig. Inspector shows broken bone references in red. Re-pick each from the bone list.
Use Bone Reference by Name
Where the rig allows, use the name-based reference. Survives index changes; pays a small lookup cost.
Validate on compile
Control Rig compile errors surface broken references. Always re-compile after skeleton edits.
“Bone references in rigs are typed by index by default. Renames break the index assumption.”
If your character pipeline involves frequent bone renames, switch the project default to name-based bone references. The cost is small; the resilience is large.