Hi @murdocc_2015 , the WaveShell plug-in is famous for causing trouble in Dorico’s audio engine. When it is missing a license, it pops up an alert window, but that alert does not get into the foreground and stays behind the Dorico window waiting for a user prompt. Because of this the audio engine comes to a standstill. So please launch Dorico again and watch out for hidden alert boxes and see what happens if you click them away.