Why doesn't the JavaScript event for Mobile Safari fire?

Question

safari

Good afternoon.
For site pages that have a "category menu", a JavaScript event is set (notifying that the visitor has seen the menu). But with Mobile Safari, problem= doesn't always work. Example: a person visits a product category
page for almost all browsers, the event is fired at about 100%, but for Mobile Safari 12/13, the event is fired at 93%. For Mobile Safari, how do you need to set a special event in the metric? PS the event fires after the page is loaded (window.onload) loading about 2 seconds. Some browsers still have about 90%, but there are almost no clicks from them (less than 1%), so I don’t mention them.