Slick slider code only works for Android - why isn't it working for iOS (portrait only)?

I have an issue here and would love your input. So, I have a page with 3 images side by side in desktop mode and landscape mode, and they need to turn into a slider on mobile, portrait. I used slick slider, the code below, added the newest jQuery link and worked just fine - they were all added in the same file, to test them: html, jquery cdn, jquery code. However, we are using a CMS, so when I moved the js code to a .js file and the jquery v3.5.1 loaded externally, it stopped working for iOS. Did you encounter a similar situation? Any ideas? Thanks!

    $slickTest = false;
    function startSlider() {    
        if ($(window).width() <= 540) {
            if (!$slickTest) {
                $(".responsive").slick({
                    dots: true,
                    arrows: false,
                    slidesToShow: 1,
                    slidesToScroll: 1,
                    infinite: true
                });
                $slickTest = true;
            }
        } else if ($(window).width() > 540) {
            if ($slickTest) {
                $('.responsive').slick('unslick');
                $slickTest = false;
            }
        }
    }

    $(document).ready(function() {
        startSlider();
    });
    $(window).on('resize', function() {
         startSlider();
    });
  });