I solved the issue by NOT using the child theme provided by the developer any more. The main theme gave no problems and with using one click child theme plugin and using that child theme, the problem is gone.
But I see it’s in the child theme. The twenty fourteen theme don’t give any problems and Klein parent theme no problems. But only in the Child theme. Thanks for helping me. I will contact the developer of the theme to help me out with this.
It is not solved. I have the problem in Safari, Chrome and Firefox. As soon as i have clicked on ‘evenementen’, the submenu on ‘MKB Maat’, ‘evenementen’ and ‘Platform’ disappears. If I click on one of the other menu items, the submenu comes back.