Hi @technick,
Clean Business Pro slider uses a full width slider. That is, the image is set as background of the div rather than a different image tag. What this does is not allow the longer images to be viewed fully on mobiles because mobiles are portrait and laptops are landscape. You can check out twentyseventeen default theme, which has same issue.
There is a mistake in our theme instructions, so I apologize for that, the image size should be 1920×1280. If you try that image, it should solve your problem, although just a bit of image will be cut on mobile view due to background implementation.
There are a few options you can do,
1. Try 1920×1280 image size or even longer( nearly 1:1 ratio or 1920×1920)
2. We can try and focus on a part of image via custom css like center of left or right(currently focused on left)
3. Best option I can see is using a different theme: Parallax Frame Pro theme. Checkout its demo at https://catchthemes.com/demo/parallax-frame/. You can email sales at https://catchthemes.com/contact-us/ and they should swap out the theme.
Regards,
Pratik
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