I noticed some of my books worked fine on iOS 26 Marvin while others were stuck on the first two chapters. The problem epubs all came from the same source (and all seem to be created by Calibre). To see if it's possible to make them work, I ran a couple of them through Sigil.
Test 1
Sigil gave a not well formed message for the epub upon opening and fixed it automatically. Sent the fixed epub to Marvin but nope, still didn't work.
Test 2
Edited the epub some more.
Tools - Restructure Epub to Sigil Norm
I also noticed it had two css files. I deleted one which contained just the following code and removed all references to it:
Code:
@page {
margin-bottom: 5pt;
margin-top: 5pt;
}
Sent the fixed epub to Marvin and it's now working as expected (including both font size and pagination)
Test 3
Tested another problem epub. Sigil did the auto-fix for not well formed documents. This time I only removed the @page css file. The second epub is also working as expected in Marvin.
Tested working on the iPhone SE2 (2020) iOS 26.0.1 and iPad 9th generation iPadOS 26.1 dev beta.
So at least for my problem epubs, there's a fix available. It's just a bit of a hassle to fix them via Sigil one by one. I think I might try if I can do a batch delete of the extra css file using 7zip and see if iOS 26 Marvin will accept that.