thx Mahesh for quick answer.
in your demo there is no anchor, just site-jumping?
loading new page also works well in our menu.
maybe i found a solution here:
https://wordpress.org/support/topic/mobile-menu-doesnt-work-with-anchor-links
Instead of: <my site>/#contact
<my site>/#services
Use: <my site>?location=1#contact
<my site>?location=2#services