Comment 1 for bug 1713986

That sounds like a bug in iOS iBooks. I dont have any iOS devices, so I
cannot be sure, but if I had to guess, I'd say it's because those
website started adding srcset attributes to the <img> tags. Presumably,
iBooks on iOS doesn't like that. You should report it to Apple.

I have added code to the recipes to remove the srcset attribute since it
is useless, anyway. https://github.com/kovidgoyal/calibre/commit/7fd413d392a2d3ca8747a5cbde3a21d30b0f45ec

 status invalid