Replying for someone else's benefit. Seems on the MacBook it was because it was on battery and low power mode. When plugged into the mains, it worked. Not yet working on iPhone which is plugged in.

I'm finding one video in particular can play intermittently on Safari (which should give a clue but I can't figure it out) but always works in Chrome import "./BackgroundVideo.css"; import Poster from '/react.svg' import Vid from '/video_480_320.mp4' export const BackgroundVideo = () => { return ( <source src={ Vid } type='video/mp4' /> ); };

It occurs when running a simulator with iOS 17. Down stepping the simulator to pre iOS 17 isn't much use if you want to release to production. For me, using React Native, patching source is not a nice option. However, as suggested elsewhere, I was able to search for UIGraphicsBeginImageContext in the code and discover that several libraries were needing updated, react-native-svg, react-native-linear-gradient, react-native-vector-icons and I had to replace the deprecated react-native-camera.