Cannot use hooks on blog page

Hi,

I'm trying to add a page hero made with Elements/Block to the after_header hook, but I can't get it working. Nothing is displayed no matter what content I add, no matter what hook I use. On the other pages it workt well, but not on the blog page.

For the next test I add the letter "x" with the before_footer hook, so you should see this "x" on the left just before the footer:
Working test page: Contact Us
Not working test page: Blogs

It's the same when adding things with hooks by code in the functions.php file. I really don't know what's going on, do you? :-)

Markus