The same problem here, after several tests, I saw that it doesn't really appear in autoplay videos without controls, even without audio, and just on iPhones, apparently on Android devices nothing has changed. I hope this is a temporary bug and it works again soon as many sites may be affected by this.

Anyway, could you share the link to the website with a working video in the background? This could help us to investigate the difference, since all the sites I know that have autoplay videos, show the same problem.