If block(s) are hidden in a Post and the post has no excerpt defined, then a Query loop using the Excerpt block does not ignore the hidden status of the blocks in the post.
I understand there are technical reasons why implementing this would be relatively complex, but the documentation should warn non-technical users of this behaviour.

The page I need help with: [log in to see the link]

I’m guessing you’re referring to something that this ticket here already covers and resolves: https://core.trac.wordpress.org/ticket/65456

According to the information there, the fix will be included in WordPress 7.1. Its release is scheduled for August 19. You have the following options:

• Install the current release candidate for 7.1. The WordPress Beta Tester plugin can help with this. I wouldn’t recommend this for production environments.
• Or install the Gutenberg plugin. That should already include the fix. I wouldn’t recommend this for production environments.
• Or simply wait for the release.

You can also test this right now in the Playground. Recreate your scenario there, use WordPress 7.1 as the release candidate, and check whether you can reproduce the issue. If not, you can be sure that the fix is included in 7.1 and works.

If you have any further questions, I’d recommend contacting the Gutenberg team: https://github.com/WordPress/gutenberg/issues/