Zoom on Macbook Air (2015) OS high Sierra ver.10.13.6

I am using Zoom logging in an online-class or joining the meeting. After 15min, my screen got frozen and I needed to force quit the Mac. I am using the iphone as a router not wifi. I can watch Yourtube videos for a long time with no issue. Is it the programing issue with Zoom app or the connectivity issue ? Please advise if anyone have the same problem. Thank you.