I’ve only seen this on my Pixel 3a/Android.
When I select an event to view, the video doesn’t fill the field–it’s only as wide as the progress bar. The video is properly sized before play starts but then reduces while playing.
And while I’m at it I find the event thumbnails on the small size when displayed in the list. It makes it more difficult to review and decide whether to play it or not and more likely I might miss something.