I'm finding MC20 to be quite stable on several different machines configured differently on each of them. MC19 was too, for that matter.
But there is one situation that has shown up several times which seems to cause it to crash (sometimes including the server, sometimes only MC GUI). On my main audio system MC Server starts on boot and stays up as long as the system is up (days). No problems there. But if I leave the GUI up for a couple of days (sometimes just one) without any audio playback activity, when I come in in the morning, hit ctrl to wake up the screen (system is up always), and then subsequently try to play something in MC (not necessarily right away), it will crash almost immediately before actually playing anything. Simply re-running the GUI resumes like nothing happened and everything plays fine the rest of the day.
It's always that pattern when it happens, but it doesn't always happen. It will happen even if the GUI is minimized (ctrl-2). I'm currently using vers 17, but has randomly done this for the last few versions.
--Bill