UI Action 'Copy Resource Plan' not available as a Related Link for Resource Plan form
The "RMUIActionHelper" Script Include was customized and missing a method.
1. Navigate to System Definition > Script Includes
2. In the Name column, search for "RMUIActionHelper" and go to the record
3. In the Versions related list, right-click the record with the Source of "System Upgrades: glide-madrid..."
4. Select "Revert to this version"
5. Click OK