I am sorry, but there’s absolutely nothing special to record – there are no related errors in console, “Variation image cloned” message is shown after I hit “Save Changes” button, but the image is not copied to other variations.

I am sorry I was unattentive. The problem is with “Set image from another variation / from this product” feature, not “Set image to other variation(s)”. And I make it just as it is described in your video – https://www.youtube.com/watch?v=lxOZl30wQms

“Set image from another variation / from this product” feature does not work again. I still can’t figiure out what’s going on. There are no messages in console and it’s still not working with default theme and all plugins disabled.