[Theme: Zerif Lite] Burger menu bug

Hello everybody

I have a problem with Zerif Lite v1.8.4.4. My burger menu bugs as shown in the video below: https://vid.me/qE3i

When I click the burger icon it shows the menu for half a second and disappears again. When I click the burger icon a second time again after it happened nothing happens until I click it again a second time then it shows again for half a second and disappears.

I have tried to remove all the CSS i’ve written to test if something I wrote caused the bug, but that wasn’t the case. I have also tried to replace my header.php with the standard Zerif Lite header.php to see if that helped, which wasn’t the case either.

Does anyone have any suggestions on what could cause the bug?

Thanks
/Mads