Gutenberg: Invalid code results in classic block not converting to individual blocks

[selectedselections]

Steps to reproduce

1. Starting at URL: My Site -> Site -> Pages -> Add new page
2. Add a classic block to the page
3. Edit the classic block as code and add some invalid code like this screenshot
4. Add more example content in a valid format
5. Try to convert the classic block to blocks

What I expected

The content within the block would be converted to individual blocks

What happened instead

The classic block will not convert to individual blocks

Browser / OS version

Chrome / Mojave 10.14.6

Screenshot / Video

See video added to notes here: 2473968-zen

Context / Source

More context here: 2473968-zen

#user-report

[rinazrina]

Similar report here 2759740-zen

I've tried to remove the invalid codes, but it's somehow still can't be converted.
I've asked the user to recreate the content in a new page in the meantime.

[rickmgithub]

User returned here asking if we had found a fix. They've provided screenshots and a lot more detail which may help #2890004-zen

[github-actions]

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