What you say would be correct if the problem could be reproduced, whether it is a beta bersion or a final version does not matter here.

I compared Will's page with mine, it's missing from Will. If you compare the page of Will with mine (see screenshots) you see immediately where is the problem, you see that it is a problem of css and Will does not have the same files as the original.
If I uncheck this:

.bx-videos-entity-video video {
    max-width: 100%;
So I have the same problem as him, and he does not have it.
I sent my original main.css file from the video module to Will 3 days ago, and I have not heard from him since. Why?

You see that Alex has given the right track, no answer either.