Anecdotally, I would agree that VNC is a common pattern. I access my Ubuntu Desktop via xrdp, and it never has problems. I access my Ubuntu Server via VNC and it is the one that hangs -- always a bit of time after I VNC into it.UPDATE: I may be wrong, but I’m beginning to see the possibility that for some reason the launching of a VNC session is the trigger that makes the VM inaccessible. My VM is running two days now and I have only accessed it via terminal in Linux or an iOS or Android app. Previously I sometimes felt the need to check the VM via the GUI and so would always click on the VNC tab and then obtain the error in connection message. If the VM stays connectable without VNC use, then it seems VNC may very well be the culprit. In the words of Arnie, “I’ll be back.”
But that's just observational. Far from conclusive.