I see a few variations of this topic on the forum, ie
I have a theory if anyone is interested.
in the setup, there is an option to “allow MSIO to have exclusive access to port”.
I think when dorico is installed, this option is enabled.
So, when you start dorico while you have something running in the background (ie, media player, Audacity, webbrowser, etc) that has already attached itself to the port, dorico won’t be able to get it exclusively and it looks like (based on your system) some users:
a) get no sound [dorico can’t get the port]
b) get sound exclusively [dorico steals the port].
Users, by restarting, closing things, other general debugging, eventually knock the port loose, and it suddenly “works”.
Anyhow, that is my theory.