Classic Block is blank when a YouTube video is part of the content

Steps to reproduce:

1. Update to WordPress 5.0.x
1. Create a new post
1. Add a classic block
1. Add a few paragraphs of text and a YouTube link such as https://www.youtube.com/watch?v=P6CyTF32K2w on it’s own line into the classic block
1. Save and publish, then close the post
1. Install and activate the Post Thumbnail Editor plugin (I tested with version 2.4.8)
1. Re-open the post

Result: the classic block is blank when a YouTube video is part of the content and the following error appears in the console:

TypeError: wp.shortcode is not a constructor

Screenshot: https://cloudup.com/c6DN2Comvz6

/hat tip hexagongirl for the original report on GitHub at https://github.com/WordPress/gutenberg/issues/12678#issuecomment-453159948