Same problem here, both on a local and online web server. It happens randomly and I can’t figure out why. One day I add an embed and it loads on both frond and back end. Then a few days later it’s not showing the embed, but just the link to the embed. There are no console or other errors.
https://www.dropbox.com/s/29j0r3wthdcosk3/spotify.png?dl=0