Sorry for this – potentially stupid – question. But I’ve wasted too much time already.
On the Target theme, there are black boxes on the /tech/ and /contact/ pages. However, when I create a new page or even duplicate them, these are gone. I just couldn’t find out where these come from. Thanks for your help.
TLDR: Go to Appearance > Elements and look for the Header Element assigned to those pages. Edit it and go to Display Rules tab where you can set the other locations you want them displayed.