Because Scenes contains snapshots of a rack at the time the scene is captured, it is possible over time for scenes to build up extra data that is no longer important. For instance, if a plugin is removed from the rack, the data for that plugin is no longer needed. It will not automatically be removed. Instead, you may Trim the rack to remove unused data.
The command is in the File menu. Trim simply cycles through all scenes in the rack, applies each one, and then recaptures it as a new up-to-date snapshot.
If you encounter a hang or crash during rack trim, you may use a troubleshooting option to see if that addresses the issue. See Trim_Delay_Ms in OPTIONS.INI.