Thank you for posting. I noticed that the title of your post mentions “AFTER EDITOR” , but in your description, you refer to “Blu-ray/UHD Creator.” These are two different products in DVDFab.
To help you accurately, could you please confirm which DVDFab product you are using?
DVDFab UHD Creator (for creating or converting videos to UHD/Blu-ray structure)
DVDFab UHD After Editor (for editing existing UHD/Blu-ray backups, including menus, chapters, etc.)