Just wanted to give people a heads up. There is an issue in 2019 R2.1 and above where if you LoadPage in the open event of an HTMLViewer using the WebKit renderer you might (will?) get an assertion error (at best) or a hard crash (at worst). Windows only.
Window.Open event is still too soon. Delay the load by a few milliseconds seems to work.
This has caused many hours of testing to figure out.