We’ve started seeing issues with our Glitch embeds where they display for a moment and then disappear. Here’s a tracking issue: https://github.com/GoogleChrome/web.dev/issues/2997
I think you can see the bug if you visit https://web.dev/style-focus/ in an incognito window.
Odd, it works for me.
I suspect your browser may be blocking scripts that the embed uses. What browser are you using?
I’m able to reproduce using Chrome 83.0.4103.61 in Incognito
Ah, I’m running 81.0.4044.141.
In that case you should email firstname.lastname@example.org and let the team know.