I just noticed that on the site that was a fresh install the video embed stopped working. I upgraded it today to 6.4.4 but it's still not showing the videos.
Are you not able to do YouTube videos or is it something else? Did you test the same at our demo.socialengine.com ?
Testing the demo is like testing a boat motor in a swimming pool. You don't know what works in open water or in the case of social engines when people are signing up, and posting multiple times and combinations. I have to look into this more. Social Engine is my highest maintenance site. It has some good features, but it's painful to manage. Like I said before it's like it's made to require people to help.
I use SE for my own site and we use it for this site so it is upgradable and usable. I've a friend who has me do their maintenance and I've upgraded all 5 of her sites without issue. All videos work fine and those sites are all social sites with real people. They host at BryZar though and I don't know the hosting configurations other than it goes by the requirements with MySQL instead of MariaDB.
Is it just YouTube or something else? Are you using the YouTube API key if using YouTube videos? Note that YouTube has a limit to their video API so if you reached that limit, the issue is on that end of things.