About Keyframe Sync Mode
When you change the duration of panels, add, delete or drag-and-drop scenes and panels, it affects the placement of keyframes.
Setting the keyframe syncing to the None option will keep your keyframes exactly where they are when you change the panel duration. You will lose keyframes not within the scene range.
Setting the keyframe syncing to the Relative to Panels option will reposition all the keyframes within the selected panel, relative to where they were placed in the panel. When a panel is deleted, all keyframes within the deleted panel will also be deleted.
Setting the keyframe syncing to the Relative to Scene option will reposition all the keyframes within the selected scene, relative to where they were placed in the panel.