Fixed Layout EPub - Problems exporting...

Hello,

I've created a comic in InDesign 2020, in which every page is a single image. Just under 100 pages of nothing but a large image on each page. I'm trying to export it as a Fixed Layout Epub. I set all the images to the lowest quality (to reduce file size), and left mostly everything on default.

So, to the problem at hand. I open my Epub in Sumatra, and encounter some unusual things.

- Certain pages will display twice (in the ereader, where there's two pages displaying at once, the same page will be shown on both sides at the same time.)

- There's always a non-existent page after my Page 14 (After I turn Page 13, there will be a blank on the left, and Page 15 on the right. I turn again, and Page 14 will display on the left with 15 on the right as it should)

- One page at the end of the document doesn't appear at all

When exporting, I DO have all-pages selected, and I initially had spread control set to "Based on document set-up", and experimented having "Disable Spreads", but it didn't make much difference.

I was at first getting an export error message about a text anchor, but I've since deleted that and no longer get the error. Still the same problem, so I don't think the anchor had anything to do with it.

If it makes a difference, this was originally a different .idd file for a different comic I'd created; I just changed the image links. The previous file had been converted to a Fixed Layout Epub using CS6 1-2 years ago. However, the page which doesn't appear in my new one is added on a new page later in the document.

Really hoping I can get to the bottom of this, and what things can possibly be causing this. I had no problem converting this same file to PDF.

Thanks in advance.