I don’t think this is Dorico’s fault, but it is an issue. On my Mojave iMac both Safari and Firefox seem to interact somehow with Dorico and cause the pitch to rise to an annoying degree. It takes a computer restart to fix it. Has anyone dealt with this problem, which I think is an Apple thing, but what do I know?
It’s not something I’ve spotted here, but the solution is to go into Dorico Preferences > Play > Audio device setup and set the sample rate again.