You fix it by adding slices to all the parts of your document.
You can also check what options are checked for HTML and Images.
You can Click on File>Export and choose "HTML and Images" as the export option.
Check if the "Include areas without sllices" is checked. If it is checked then your preview should be working fine.
If its not, then you could possibly export one of the pages with that particular option(include areas without slices) checked.
After that, your preview should be working fine.
Thank you very much! That was really what i was looking for. Never thought
of doing that
glad to hear that it fixed your issues