There is no issue on your site I have checked your site on desktop as you said:
The Quick View
Buy it Now
And add to cart popup
All is working fine I made a video for you please watch it first: https://streamable.com/fnb79m and then try to disable the cache plugins you are using and then contact your service provider (Hosting) to flush the server cache completely and then check back to your site after clearing the browser cache.
Regards 8Themes Team.
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.