Alright, I have checked your issue and found that on mobile when the next image slide, in between, the desktop image appears just for a moment. It is because you added a mobile image using an image element in the slider as you can see in the image: https://postimg.cc/rdrGvv32 and the desktop images are set on the slider background so that’s why when the elements scroll or slide, the background thing will appear until the elements scrolls or slide completely. The visibility option is for the elements like if there is a text that you don’t want to show on mobile you can use this option but this option will not work for the backgrounds as you can see in this image: https://postimg.cc/3y1rJwPX
So the thing is if you want to show a different image for mobile and desktop you have to create two sliders and then set both sliders on the site. I can see that you are using an element in the page to set the slider as you can see in this image: https://postimg.cc/WdvC5c4C now to show different sliders you have to add two sliders on the page and in the column settings of the page builder you can hide the slider from the specific devices. I have made a video for your please watch it complete for a better reference: https://streamable.com/q6ihwx
Regards 8Themes Team.