I tried playing with “screen edges”. Disabling corner actions did not resolve the issue. Interestingly, reducing “edge barrier” to 0px got rid of the cursor “pausing” when moving between the screens, but it did not resolve the screen freeze issue.
However, I read your post Problem with installing Manjaro Arm on Raspberry Pi5 - #14 by Sam_Fisher and tried using X11 instead of Wayland. And that solved the problem. Thank you very much. 
I can confirm your comments about Chromium’s performance. “Webgl aquarium” has the fish swimming at around 20fps under Wayland and 55-60fps under X11.
Interestingly there are similar differences with KDE running on RPI OS. However there is a problem with flickering screens when running with two screens with X11 with RPI OS.