sometimes the images aren't loaded and browser shows error icon until the page is scrolled about unveil

[paolobenve]

Well, I checked more specifically, it's not for the cache...

What is then the reason of this behaviour?

[paolobenve]

I modified the title: the problem is that, randomlessly, some visible image isn't unveiled until the page is scrolled. Why?

[jakmedia]

I get the same behavior when using jQuery 3.3.1. It works as expected on older versions of jQuery for me. I'm not sure how to fix this though.

[jakmedia]

SOLVED – If you are using jQuery 3.3.1 you need to change the second line of your Javascript code.

$("img").unveil(200, function() {
$(this).load(function() {
this.style.opacity = 1;
});
});

Change the line of code in bold above to this:

$(this).on('load', function() {

Worked for me. No more Javascript errors in the browser.