Course Presentation link to next slide shifts on different devices


I created a course presentation with multiple slides and one interactive video on each slide in Moodle. I added a link (overlay) on top of the video in the bottom right corner to go on the next slide by clicking on this. On different devices like laptop, mac, android smartphone it's working fine but when viewing it with my iPhone the overlay shifted away and isn't in the spot where it should be.

I disabled all customized CSS rules but the problem is still the same.

I attached you some images where you can see the overlay. The first image is in a vertical position on mobile and the second image is in a horizontal position on mobile. Normally the overlay should lay over the blue button in the second image.

When creating a new course presentation and placing the same type of overlay in there, it seems to sit on the right spot in both, vertical and horizontal. But way is it then shifted in my first element? Any ideas?