Gutenberg produce BROKEN html output

[EldarAgalarov]

How text looks in gutenberg editor:

https://i.imgur.com/ppbPMg7.png

How output result looks:
https://i.imgur.com/YO3NGYT.png

Part of the text are gone
closing "strong" tag also is gone, producing WRONG html markup

Please fix it.

Wordpress 5.0.1

[EldarAgalarov]

How to reproduce:

Put h2 block with text:
Next put paragraph block below h2 with text:
And what you see on output? only h2 but not paragraph block!

Next, add paragraph block above h2 block with text:
Now last paragraph is shown but it's WRONG - part of words and punctuation are lost! So there are at least 2 bugs!

[designsimply]

Aha! Thank you for the extra information, I was just about to ask about how this content was first created and to clarify about the screenshots.

I was trying to see in the first screenshots and I noticed this:

became this:

And I saw the the ending strong tag was missing for the part of the text that begins with "63.91%".

However, trying with the example text you provided is much better and I will add the Needs Testing tag for that so we can look in more detail.

Can you tell also tell me a little more took to get to this point? Did you write it with Gutenberg directly? Did you write it before upgrading to 5.0.1 and then press the "Convert to Blocks" button? Or did you copy the content from elsewhere such as a word processor or a different post or even another web page?

[designsimply]

I am not sure yet if it's relevant, but may I also ask if you have any plugins installed which modify content in any way? It's possible to have a plugin conflict, and we should test from our side first without plugins but it's also a good idea to make a note of them if you have any.

[EldarAgalarov]

I'm writing in with Gutenberg directly, without content conversion from classic editor into blocks. Just copy-pasting text from Notepad-like text editor.

[EldarAgalarov]

I disabled all plugins and it not helped. In general i'm using WPML and Yoast SEO now.

[EldarAgalarov]

I found that if Gutenberg doesn't produce HTML comments like then seems it works fine. HTML comments in some ways broke text output.

[EldarAgalarov]

This issue related with #13404

[designsimply]

Thank you so much for the follow-ups! I researched this and found that #13404 was closed as a duplicate of #12672 and there is a request in that issue to re-open the case at https://core.trac.wordpress.org/ and I wanted to leave a note here with the status that I found.

[SergeyBiryukov]

Tracked this down to an issue with WP_Block_Parser, let's continue the discussion in #13655.