Hi Mike,
thank you very much for your quick response!
I looked into the child theme before, but didn’t find a footer.php. I didn’t do the linkage between the header.php and the footer.
But since you mentioned it I removed the header.php and the footer is back on some pages (though not on all). But definitely there is a link between the missing footer and the header.php.
I guess I have to dig a bit deeper to find the actual root cause.

BR Christian