PS: My apologies for my short reply, I'm busy at the moment. If I have got more time again, I anyway will try to use Ardour 5 again. Assuming it should be unstable, I perhaps won't spend much time in troubleshooting, but at least would try to find out how to reproduce the crash and at least run Ardour from command line. However, building Ardour is time-consuming, so I unlikely will find time to rebuild it with debug symbols.