Fancybox changing the look of my own slider?

Question

JavaScript

I wrote my own slider, the task of which is simply to scroll through images on click

1. My slider is wrapped in a .slider class
   
2. I put a Fancybox gallery on each picture of my slider so that the pictures of each slider can be viewed in full screen mode.
   
3. If you open an image using fancybox, then scroll somewhere inside the fancebox and then close it, then fancybox returns the image to the place of the slider, while changing the appearance in a way that is incomprehensible to me - the navigation buttons of my slider disappear , and in general, the previous functionality of my slider can no longer be returned - only reloading the page helps.
   
4. I looked in the DOM tree and I don’t see any changes at all in order to somehow understand how to deal with this effect. Maybe it's virtualDom
   

on this site - the second slider cottages
https://www.terveranta.ru/