How to reproduce:
  1. Refresh the page.
  2. Once the button appears, click it.
  3. Watch for where the video first appears, look for it appearing in the lower-right corner before it re-renders to take up the full container.
  4. You may need to repeat these steps a few times before you first see it.
When does the bug happen:
OS/Browser HLS Library Container format Aspect Ratio Hidden Via Shown Ahead of Loading Reproducible?
iOS 15.5 VHS M3U8 Portrait display: none 1 ms YES
iOS 15.4, iOS 14 VHS M3U8 Portrait display: none 1 ms NO
iOS 15.5 Native M3U8 Portrait display: none 1 ms NO
iOS 15.5 VHS MP4 Portrait display: none 1 ms NO
iOS 15.5 VHS M3U8 Landscape display: none 1 ms NO
iOS 15.5 VHS M3U8 Portrait opactiy, visibility, width/height 1 ms NO
iOS 15.5 VHS M3U8 Portrait display: none >500ms NO
Intermittent issues:

Unfortunately, even when following the steps above, this issue is still intermittent. Sometimes it doesn't happen, and sometimes there will be long stretches of it not happening.

Possible related issues:

When hiding and loading videos using other methods, I've sometimes observed other issues in iOS 15.5 where the video will load either much larger or much smaller than the video element before resizing to correctly fill the element (similiar to how in this error, it loads in the wrong location before re-rendering).