When running jitsi, the main interface screen is completely blank. A big grey nothing. After a significant amount of googling on duckduckgo, I eventually found the answer in section 4.12 of the xmonad FAQ
This is because Java has a list of non-reparenting windowmanagers hardcoded in it and xmonad is not on the list. The solution to the problem is simply to set the
JAVAAWT_WM_NONREPARENTING environment variable when you run Jitsi.
Here is how to run Jitsi on xmonad if you want to be able to see the GUI properly.
$ _JAVA_AWT_WM_NONREPARENTING=1 jitsi