Embed a URL error on the thumbnail

[utamayo]

Many times when I add a embed URL the thumbnail image is the default error image:

URLs with thumbnail errors:
https://m2.material.io/
https://m3.material.io/
https://romannurik.github.io/AndroidAssetStudio/index.html
https://www.appicon.co/
https://java-design-patterns.com/patterns/

Any suggestion why is this happening?

[DanielSmithGK]

Thanks for raising this, I have the same issue, e.g. with https://app.powerbi.com.