Draggable elements don't work

Hi folks, me again!

Some mechanism of drag and drop elements doesn't seem to be working in 6.8. Not sure what the specific feature in use is, but see below for a reproducer

I've experienced it in the wild on the outlook web app (dragging mails to a folder and moving events in the calendar).

The symptoms are that the browser freezes up for a few seconds, then freezes up for a few more seconds if you still have the mouse held down, then when you release the element the move doesn't take effect.

I can reproduce on this demo: https://codepen.io/Goldfsh/pen/zBbOqm

On stdout I see WebContentsAdapter::updateDragAction was not called within 3000 ms.

I'm not on the latest commit of the 6.8 branch sorry, still on 3f4790463cc5 of the qt5 repo. I haven't been able to test newer builds because I keep getting Renderer process crashed (status 5), not sure if that is my build or something on the branch.