An error message stating "Sorry, we could not embed that content." appeared.
Chrome v70
Gutenberg Version 4.0.0


Wanted to add that I tried it with different embeds and got different results:
1. Instagram link:
Error saying it can't be embed.
Front-end shows it correct, though:
2. Spotify link:
No error:
3. Facebook link:
Error too big to be displayed in the correct area.
Front-end shows it correct, though:
4. Twitter link:
No error:
Desktop:
OS: Mojave 10.14
Browser: Firefox
Version: 62.0.3
Additional context:
Atomic site with only Gutenberg installed, besides Jetpack
Status update on all Embed Blocks
TLDR;
Working completely as Expected
YouTube
Twitter
Dailymotion
Flickr
Imgur
Issuu
Polldaddy
Reddit
Not working as expected(Problem): CNE - Could not embed
Embed (Not sure what other URL works here)
WordPress(Publish Only)
Facebook(Both)
Instagram(Both)
Spotify(CNE)
Soundcloud(Editor Only)
Vimeo(Both)
Animoto(Editor Only)
Cloudup(Editor Only)
College Humor(Both)
Kickstarter(Both)
Meetup(CNE)
Mixcloud(CNE)
Photobucket(CNE)
ReverbNation(CNE)
Scribd(CNE)
Slideshare(Editor Only)
SmugMug(Editor Only)
Speaker Deck(Console Error)
Ted(Editor Only)
Tumblr(Publish Only)
VideoPress(Editor Only)
WordPress.tv(Editor Only)
Noticed on a poor internet connection it blanks out like this for embeds in the editor

And the publish preview is empty
Also noticed this weird behavior sometimes
Editor Preview

Publish Preview

Youtube
Tested with URL: https://www.youtube.com/watch?v=5dsGWM5XGdg
Editor Preview:

Published Preview:

Tested with URL: https://twitter.com/automattic
Editor Preview:

Published Preview:

Embed
Tested with URL: https://en.wikipedia.org/wiki/Cat
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Couldn’t figure out a URL that could work here besides one valid for another more specific type of embed
WordPress
Tested with URL: https://testing201814.blog/
Tested with URL: https://testing201814.wordpress.com
Tested with URL: https://testing201814.blog/2018/10/23/
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Tested with URL: https://testing201814.blog/2018/10/23/gutenberg-tiled-gallery-block/
Editor Preview:

Published Preview:

This seems like it’s intentional but I expected embedded content similar to the Editor Preview from at least https://testing201814.blog/2018/10/23/
Dailymotion
Tested with URL: https://www.dailymotion.com/video/x6w7aph?playlist=x63q3a
Editor Preview:

Published Preview:

Facebook:
Tested with URL: https://web.facebook.com/WordPress/
Tested with URL: https://web.facebook.com/WordPress/posts/10156301634992911?__tn__=-R
Editor Preview:

Published Preview:

Instagram:
Tested with URL: https://www.instagram.com/_codingblog/
Tested with URL: https://www.instagram.com/p/BpiEuYRhsev/?utm_source=ig_web_button_share_sheet
Editor Preview

Publish Preview: N/A
Spotify:
Tested with URL: https://open.spotify.com/playlist/37i9dQZF1DX2A29LI7xHn1
Tested with URL: https://open.spotify.com/search/results/drake
Editor Preview:

Publish Preview: N/A
Soundcloud:
Tested with URL: https://soundcloud.com/lil_peep/lil-peep-ft-xxxtentacion-falling-down
Editor Preview:

Publish Preview:

Flickr:
Test with URL: https://flic.kr/p/2cpgoHs
Editor Preview:

Publish Preview:

Vimeo:
Tested with URL: https://vimeo.com/channels/staffpicks/295354277
Editor Preview:

Publish preview:

Animoto:
Tested with URL: https://animoto.com/play/WmGs0SgMeHvBMur0fL68rw
Editor Preview:

Publish Preview:

Cloudup:
Tested with URL: https://cloudup.com/if61tFHyBgA
Editor Preview

Publish Preview

College Humor
Tested with URL: http://www.collegehumor.com/video/40004082/the-girl-with-a-birthday-month
Editor Preview:

Publish Preview:

I think this one specifically fails due to the URL being not over https and suspect this would apply to any http embed URL.
Console log:
Mixed Content: The page at 'https://jetpack-gutenberg-testing.mystagingwebsite.com/?p=44&preview=true' was loaded over HTTPS, but requested an insecure resource 'http://www.collegehumor.com/e/40004082'. This request has been blocked; the content must be served over HTTPS.
Funny Or Die
Tested with URL: https://www.funnyordie.com/best-of-the-web
Tested with URL: https://www.funnyordie.com/best-of-the-web/2018/10/29/18040122/big-asian-naturals-supermarket-vice-parody-documentary-jamaal-sedayao
Tested with URL: https://www.funnyordie.com/2018/10/30/18040648/dumb-spanish-dubbing-halloween-silence-of-the-lambs-childs-play-it
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Imgur
Tested with URL: https://imgur.com/gallery/v7Qs8ND
Editor Preview:

Published Preview:

Issuu
Tested with URL: https://issuu.com/mymagazinebymollymy/docs/my_magazine_fall2017_finaloct18/34
Editor Preview:

Published Preview:

Kickstarter
Tested with URL: https://www.kickstarter.com/projects/1683809116/manjits-kitchen-and-bar?ref=discovery
Editor Preview:

Published Preview:

Meetup.com
Tested with URL: https://www.meetup.com/Kingston-WordPress-Meetup/events/smvthpyxpblb/
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Mixcloud
Tested with URL: https://www.mixcloud.com/melodicdistraction/born-to-roll-1st-birthday-special-october-18/
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Photobucket
Tested with URL: http://photobucket.com/gallery/user/bstevens2002/media/bWVkaWFJZDoxNjQ4MTUzNDA=/?ref=
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Polldaddy (Now Crowdsignal)
Tested with URL: https://poll.fm/10151656
Editor Preview:

Published Preview:

Tested with URL: https://www.reddit.com/r/webdev
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Tested with URL: https://www.reddit.com/r/webdev/comments/9rkm4f/beginner_questions_october_26_2018/
Editor Preview:

Published Preview:

ReverbNation
Tested with URL: https://www.reverbnation.com/collection/186-mellow-beats
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Screencast
Did not test
Scribd
Site not working atm….

Tested with this URL: https://www.scribd.com/article/391724241/
Editor Preview: “Sorry, we could not embed that content.“
Published Preview: N/A
Slideshare
Tested with URL: https://www.slideshare.net/reidhoffman/blitzscaling-book-trailer-118631898
Editor Preview:

Published Preview:

SmugMug
Tested with URL: https://nelli.smugmug.com/Daily-photos/i-bXKH8bz
Editor Preview:

Published Preview:

Speaker Deck
Tested with URL: https://speakerdeck.com/maltzj/code-reviewing-like-a-champion
Editor Preview:

Published Preview:

TED
Tested with URL: https://www.ted.com/talks/ken_robinson_says_schools_kill_creativity?referrer=playlist-the_most_popular_talks_of_all
Editor Preview:

Published Preview:

Tumblr
Tested with URL: http://iglovequotes.net/post/179598785847/httpiglovequotesnet
Editor Preview:

Published Preview:

VideoPress
Tested with URL: https://videopress.com/v/kUJmAcSf
Editor Preview:

Published Preview:

WordPress.tv
Tested with URL: https://wordpress.tv/2018/07/04/matt-mullenweg-a-summertime-update-keynote-and-qa/
Editor Preview:

Published Preview:

FYI youtube Embed not working in wpcalypso, Noted here -> https://github.com/Automattic/wp-e2e-tests/pull/1670
Also added here:
https://github.com/Automattic/wp-calypso/issues/27708#issuecomment-445372797
But I have a user whose Getty images appear to all be broken by the recent update. And the only way to fix it is by manually updated each specific Getty embed.
After the 5.0 update and switching AT sites to Gutenberg, all of this site's Getty embeds are broken:
Embeds are now all display an "Image not found" error like this:

To fix it, each individual image has to be edited in the Classic Editor and updated. Which is extremely labor intensive. For example, this is the process to fix the images in a single post:
8153499-hc
Can we please open an issue per broken embed? For easier viewing I've also created a milestone to add this to. Reports are very much welcome if you're unable to find existing issues.
Can we please open an issue per broken embed? For easier viewing I've also created a milestone to add this to. Reports are very much welcome if you're unable to find existing issues.
@gwwar sure, I'll work on this... We also still have -> https://gutenpackembeds.mystagingwebsite.com that has all the blocks, I'll try a put this somewhere for reference