That tells me that the VSTAudioEngine process is still running, but it most likely is deadlocked. So when that happens please open the ActivityMonitor app and have a look for a process called VST Audio Engine. I guess it is marked as “not responding”. Now, in the Activity Monitor at the top of the window is a round icon with three dots in there. Highlight the VST Audio Engine process and then click on that mentioned icon. From the pop-up menu choose Sample Process. Follow the instructions and please post the created file (after zipping) here.
When you then force quit the VST Audio Engine process (highlight the process and click on the icon with the x inside) you should be able to start Dorico just like usual again. Or does it not do?