Here is the previous thread: “Header video suddenly not displaying” started on July 7.
I have updated my site to the very latest X and Cornerstone available as of today. Videos still do not display as described in the previous thread when any version of Jetpack is used beyond 9.8.1.
I did testing as instructed on July 17 and supplied feedback that everything works fine with the latest Wordpress 2021 theme and Jetpack 10.0. When reverting to X, all videos render as blank page space again. I have to rollback to 9.8.1 to get videos to display.
Jetpack [posted to Github with info about replicating the error] on July 20 using my screenshots (https://github.com/Automattic/jetpack/issues/20412) and they determined the issue is with X since it was only reported when X is active.
The issue was closed unresolved on August 14, after the final advice to wait for your own look into the issue. Meanwhile this thread has appeared on this forum, but the support response seems to be that the “plug-in author” is working on it. They’re not.