If you encounter this freeze again, please run Activity Monitor, select the Dorico process in the list of processes, and from the cog menu in the toolbar choose Sample Process, then zip up the resulting text file and attach it here. Restart Dorico and do Help > Create Diagnostic Report to generate a set of diagnostics, and upload them too, together with a note telling us the time (as close as you can recall) that Dorico froze up.