Thanks for the reply. We've done all of the troubleshooting that I can think of. They've tested the site in updated versions of Microsoft Edge and Chrome on different computers and different internet connections. They've cleared their browser cache and cookies, and tried private/incognito browser windows. All Javascript and CSS on the site is working for them. The left click to zoom feature on product pages is the only issue. Their cursor turns into the magnifying glass icon, but left clicking doesn't do anything.
This could affect site visitors when we launch the site, so it needs to work even in browsers that aren't up to date. I've tested in Chrome, Firefox, Edge and Opera with and without the latest updates installed, and it always works for me.
I stopped using CSS scroll-behavior: smooth; for anchor navigation because I noticed that it doesn't work if the Visual Effects setting 'Animate controls and elements inside windows' is disabled for Windows operating system users. Is the left click image zoom function similar? Is there a function built into the operating system that has to be activated for it to work?