They've written their own scrolling logic (why...) which involves cancelling or stopping propagation of the normal gesture and events. They broke scrolling on purpose and accidentally broke other things in the process.
I wish there was a single flag to disable all that crap such that developers had to consider users who have the flag set, better still if it's on by default or behind a permission check
'This site would like to hijack your scroll wheel/touchpad', it's genuinely infuriating.