Hello, @RoDaAmsterdam14,
Yeah, that is the main issue, let me try to explain to you, the desktop size is larger than the mobile screen sizes, and the images you chose for your slider are very large images and do not properly design to fit on the mobile screen.
If you simply set it back as Cover then it will be fine again on the desktop version but on mobile, it will generate the same issue for you as you have before.
So the proper solution for this is to create another slider for the mobile version with different images properly fit for the mobile revolution and hide the desktop slider on mobile using Column Responsive settings: https://postimg.cc/RWpV5JXL and vice versa for the desktop version.
Hope this helps.
Regards 8Themes Team.