Playback of any kind of HD H.264 MP4 files (720p, 50fps) could randomly cause a stalled image. Playback does not stop in such a case. Image is frozen/stalled. Audio goes on. Timeline goes on. By tapping play/pause or scrubbing in the timeline, the playback recovers. It could also happen, if you are scrubbing in the timeline, especially to areas not loaded already (progressive MP4 download). Behaviour is always the same: image is stalled/frozen, audio goes on.
To reproduce: use example project https://developer.apple.com/documentation/AVKit/playing-video-content-in-a-standard-user-interface Example file: https://www.keepinmind.info/test.mp4