Describe the bug
in Gutenberg 3.8 where the classic editor doesnt show in the backend if a php rendered block is added just after the classic editor block.

It seems to be something to do with how the comments work. For example my php rendered block would be stored in the database like this:
<!-- wp:my-blocks/block-custom /-->

This causes the classic editor not to render, however if you change the comment to
<!-- wp:my-blocks/block-custom --><!-- /wp:my-blocks/block-custom -->
Everything will render in the editor correctly

Going back through the commits - it seems that it was caused by the new parser ( #8083 )

If my description you can see the conversation here in slack - https://wordpress.slack.com/archives/C02QB2JS7/p1537188435000100

To Reproduce
Steps to reproduce the behavior:

1. Add Classic editor block add some content
2. Directly after add the latest posts block (its a php rendered block)
3. Save the post
4. Refresh to see that the classic editor is not visible even though the content is in the database.

Expected behavior
Classic editor should be visible

Additional context

• Gutenberg 3.8