Hello. First I noticed problem on my site with iphone 6 (and no problem on demo-site). So I supposed that it';s some my template conflict... Than I checked it with iphone 4 (in google chrome) and noticed problem in ES-demo too.
1) use mobile portrait view (iphoe 4 recomennded)
2) navigate to single photo page (not popup):
https://crimson-land.ru/photos/photos/48146-sobaki-obglodali-mertvoj-devushke-litso-03-04-2019
Result: There is some padding in right area.
The more devise resolution (screen size) the bigger padding.
But in ES-demo is lower, So I can see problem only on iphone 4 and 5.
Thanks.