Hi David (CPH54a )
1. Open PD
2. Edit Workspace, Project in Tracks
3. Select to display Chapter Room and Chapter track
4. First Chapter displays
5. Move the track slider in your project to a new preferred position. Use Preview to check.
6. Move to the Chapter Room, icon button on the bottom right, set just to the left of the Preview play button. Click it. (Set current frame as the chapter thumbnail)
7. You have now reset the thumbnail image.
Ok, You might have problems with this but it should work and should display the thumbnail in Menu designer later.
Dafydd