This ended up being an issue specific to the latest version of iOS 12.4. The problem was that I had a function that was changing the URL of some images being loaded using the window.resize trigger. This was better than the CSS resize for quality, but I have since moved all of this in to CSS. But this call still remained…silent and lurking. It caused no harm on previous versions of iOS or Android, but having this in place caused the Twitch onContext callback to fire repeatedly and resulted in a blank screen.
If someone has this in their code, remove it:
$(window).resize(function() {
adjustSize();
});
Thanks again for the very useful, “nope,” @BarryCarlyon!