I myself sometimes encounter a problem in my daily work where I am restarting Dorico via the debugger, which means that the audio engine doesn’t quit, and instead keeps running. When Dorico starts up again, it finds the running audio engine and reconnects to that. However, at that point, I never get any audio output from Dorico. To restore audio, I have to quit Dorico cleanly (so that the audio engine also quits), or manually quit the audio engine, then restart Dorico again.
Obviously this kind of situation shouldn’t occur on your computer because it shouldn’t be possible for you to restart Dorico without the audio engine closing and being reopened, but perhaps somehow that is what’s happening.
If you encounter this situation again, I would recommend quitting Dorico, then checking in Activity Monitor that the VST Audio Engine process has also ended; if not, then quit it. Then restart Dorico and I would expect audio to be restored.