Menu disappears when plugin loads 2

I accidentally clicked on resolved on the previous post. But it was not resolved 😉
Can you please have a look at it.

If I activate this plugin it gives troubles with my main menu.
If the page is loading, then as soon as the plugin loads the main menu disappears. When I deactivate the plugin the menu is back again.
This seems strange to me. I already tried to deactivate other plugins to see if there is any incompatibility. But it doesn’t look like it.

I deactivated the plugin for the moment, but would really like to start using it again.

The page I need help with: [log in to see the link]