Bug on Mobile

Hello,

 

I'm testing a few courses on my LMS, via a Samsung tablet.

 

I've set up a slide in which the user has to click on 4 items to see content. Once those items are visited, the NEXT button (hidden) appears.

Same thing with the next slide, except the user has to click on 4 items, and see the 4 related slides, before he comes back to the slide and the NEXT button appears.

When I'm done viewing slides and I try to go back by clicking on the PREV button,  the NEXT button disappears on the slides already visited.

Anyone could help me fixing this ?

It seems to work on other projects but not this one and I can't figure out why !