Hi Jonathan,
Just wanted to touch base with a quick followup.
I exported a test widget with 'Use WebKit graphics acceleration' unchecked.
This made all the difference!
I added the newly exported widget to iBooks Author, and published a test version with iTunes Producer. I downloaded the new version from Apple Books and previewed it on my iPhone.
I'm so happy to report that it is working much, much better! I wouldn't say it was as smooth as butter, but it is now working passably well on iPhone, and that is totally ok with me. With no major stutters, no disappearing tempo button, and no crashing. As far as I'm concerned this is now working! So thanks so much for pointing me to that important setting change, it was a huge help! I also tested on my iPad and it is working absolutely flawless (which is to say, even better than it was!).
I did have one question though:
This new widget, despite running much better now, is flashing a white screen when it loads the widget while viewing in Apple Books.
I did some searching in the Hype Forums and I found this article from December 2014 posted by Daniel on the white flash issue. And I also found mention of the white flash issue in this article that states that Hype has built in support for suppressing this white flash.
Do you have any ideas on what I might have done to trigger this white flash (as far as I know I didn't make any other changes other than unchecking that WebKit setting, so it seems pretty random that I'm getting the white flash now). Or do you have any advice on the best way to manually suppress the white flash now that it has surfaced?
Thanks again and all the best!