Thanks for posting about this — it definitely sounds like odd behavior.
I tried to reproduce this issue on my end by uploading a bg video via Safari. After transcoding the bg video played as expected on the live site.
What sites are you seeing this issue occur in? When did it start occurring? Can you send me the site Read-Only links please?
Can you please try the following?
(1) Try to reproduce the error while being logged into Webflow using Incognito mode with browser extensions turned off: https://support.google.com/chrome/answer/95464?hl=en
(2) If the problem persists, please take a screenshot of your Console and send it to me: https://developer.chrome.com/devtools/docs/console
Could you please let me know what browser version you’re using by sending me your information from this page?
There should be a small share link when you visit the page which you can send to me.
Thanks in advance!