weird audio playback issue

Hello, I have a weird issue when playing back music in Dorico.
Sometimes one part jumps up half a tone away from its real pitch.
Let us say I have a fugue with one oboe, two clarinets and bassoon.
I play back and suddenly the first part (oboe) jumps up half a step, making the playback sound horrible.
Sometimes the music jumps back to normal. I have a Midi keyboard connected. Sometimes, during the weird playback, I can pull one of the two wheels half way to correct the out of tune instrument. Sometimes not. In case it was this keyboard interfering, I disconnected it - which did not solve the problem.
Sometimes, when I play back a full orchestra set, same things might happen: somewhere in the middle of the piece f.e. the first bassoon jumps up half a tone…
And now the really weird thing: this happens in Sibelius too.
Is there anybody with an idea, why this could happen?
I am on macOS 10.14

This sounds like the system sample rate is changing from 48k to 44.1k (or vice versa), so check to see if you have any other audio applications running that might be changing it. If you connect BlueTooth headphones then they may cause a change in sample rate.

If it happens again, write down the approximate time and close Dorico (shutting down Dorico just makes sure that the log files get correctly flushed).Then start it again and do Help > Create Diagnostic Report. That creates a zip file on your desktop. Please send to ‘u dot stoermer at steinberg dot de’ plus the time that you wrote down.

Paul, thank you for your reply.
I don’t actually have other sound devices connected (also my MIDI keyboard is a plain input device).
Still I checked settings in Dorico preferences and in Audio MIDI Setup control panel on my Mac. Everything is set to 44.100 sample rate.
The weird thing is, that only one instrument in a score changes pitch, not others…
I will report if it happens again.

Thank you Ulf, I will remember your advice and will send a diagnostic report, once it happens again.

If it is only one instrument, then it has nothing to do with the system sample rate.
Really weird, but then Dorico must be sending wrong MIDI notes to the audio engine,
or do you have pitch bends in your score? Could be that a pitch up command gets sent
but somehow the pitch down gets lost.

yes, and this is bothering me since years actually… I know in theory, what a pitch bend is, but never use MIDI commands at all in my daily routines.
There is only one thing I could think of: once, as an experiment (I was still using Sibelius) I changed the pitch (I think in Audio Engine Options) from 440 Hz to 415 Hz (half a step down), but I can’t think, how this should have been stuck in my audio system of the computer.

But changing from 400 to 415 affects the whole system and not just 1 player, so that can not be it.

Do you have a MIDI keyboard with a pitch bend wheel, which might be sending unwanted data that is somehow getting into one MIDI channel of the VST, and affecting just that one instrument’s playback?

Yes Rob, my MIDI keyboard has two wheels, and they do seem to have some functionality (pitch bend?). I might inadvertently have touched them, or they do might have a fault, as you suggest. Strange thing though, even after unplugging the device, the problem sustained.
May be it would be best to somehow disable these two wheels, I only ever need to use the actual keys and the octave shift switch.