nrevolution slider and menu in Avada theme not showing on iphone

We are encountering an issue where iPhone users are not able to properly view our website. The Revolution Slider (Slider Revolution) shows as blank white or not there at all, and the menu (which converts to a drop-down on mobile view) is simply not there. This has proven to be extremely troublesome for iPhone users trying to make their was to our “Shop” menu option in order to get to our online store.

We use the Avada theme and our website is https://www.shopUAL.com
We had an individual (who we no longer have contact with) create the site in WordPress and I now manage it with limited web design knowledge. The website appears to work fine in Safari on my iMac computer and on a Samsung phone, and works on some iPhones as well. I can not find a pattern for which iPhones it does and does not work on.

Thank you for your help!