If the name of a main menu item starts with the complete name of another main menu item, granting a role access to one of them, and not the other, is impossible.
For example; if you have to main menu items like:
Klanten
Klantenpanelen
It is impossible to grant the role of “Klant” access only to Klantenpanelen, and not to Klanten.
At least that happened in my design, and changing the name from Klantenpanelen to Klantpanelen solved it.