I started investigating because an own application frooze irregularly when I tried using QWebEngineView::load in 2 parallel views when the load calls where made approximately at the same time.

Found out I can reproduce the freeze in the webenginewidgets\browser example. Start the example and click through the bookmarks on top very quickly. It's a little easier when it's in debug. But also works in release when the user has gamer-reflexes. It's not working when just clicking the same link repeatedly. One has to click different bookmark links in a row. Usually takes me a few seconds to get a freeze.

Freeze comes in 2 different flavors. First one still shows last drawn image, but it's no longer possible to move the Window or resize or click anything. Just doesn't react at all. Second freeze still allows moving the Window but the drawing is now white.

It could be reproduced on a second computer with the same example (it was a little harder there - and that computer is faster - so very likely something timing related).

I've attached a callstack as image.