I just experienced this issue as well but from another angle. My desktop does not have any touch screen monitors however when I remoted in from my work laptop that did I experienced the disappearing mouse. I was able to get it back after rebooting the desktop. What is weird is that I manage my VMs all the time when RDP in to my desktop from the work machine (without touching the screen)
Ubuntu VM as well so RDP wasn't an option. Unraid 6.4.1
Hopefully a fix will come soon!