Poor/slow video on Zoom
I have Zoom 5.1.422789.0705 on Ubuntu 20.04. I have times when Zoom locks up and sends an "unstable internet connection" message on my monitor. The thing is that when I test my internet speed my connection is good. My conclusion is that Zoom will lock up if OTHER connections are bad on a conference call. Meaning that the problem is not necessarily on your computer (other than the incorrect message about unstable connections).
The other thing is that Zoom seems to work better if the window is small (not full screen).