Since today, for a reason I ignore, everything on Dorico is sounding about one tone too high. I checked in the Playback options and my A is tuned at 440 Hz. It’s the same issue for all my project with any VST. It’s the same if I create a new project. Everything else in my computer is fine, including Sibelius playback (I have an iMac 2029 with Mojave). When I export audio the tuning is fine.
Dan is right. Most likely some other app changed the sample rate in the background and Dorico did not get notified about it. To fix this, go to Edit > Device Setup and change the sample rate to some other value, wait 3 seconds and change it back to the value before. After that playback shall be “in tune” again.