Hello,
Back to your words, the problem may be caused by content inside the secondary menu or imported “multiple headers”.
If It is in “multiple headers” you need to resave each of them. And add secondary menu one more time. If the problem persists even after that, let us know what exactly menu is selected to display at the header > secondary menu element – https://prnt.sc/tsuRWjI6nxnF Another our specialist will try to solve the problem, but it will not be fast, unfortunately.
Regards