I think I might have an idea of what this could be. When you first load the a project that contains a video into Dorico, the audio track is extracted and saved to a temporary directory on disk, and if required, it’s resampled according to your current sample rate. If the system sample rate then changes then the audio track won’t be playable. Before you start Dorico try going to the folder ~/Library/Caches (I think it might be Edit > Go to Folder from the Finder) and delete Dorico 3 in there. Next time Dorico runs it should regenerate the video soundtrack with the current sample rate.