One issue I've suffered for a while, but I haven't posted it before because of... laziness, I suppose.
Some web pages which contain text-boxes, "quotes", "code-boxes" or similar ones stop their own rendering. It's somehow as if you only got as definitive the "fast-mode" the device use while dragging.
A good page to test:
this one in the Calibre>Editor forum. (I also paste its direct url:
https://www.mobileread.com/forums/sho...d.php?t=247023).
Just open that page and drag it downwards. When the code box is the main item in the middle of the screen, all the page is rendered nearly empty. All the text is missing.
When you clearly pass that code box area, the webpage is rendered fine again.