Dorico pitch varies wildly

Now and then, sometimes frequently, the pitch of an instrument suddenly rises about a quarter tone, then returns to normal. The clarinet is the most obvious one, maybe the only one. I’m not sure. But it goes way out of tune. (I am a piano tuner, so there is no doubt about this.)
I have been careful to shut down all other sound-generating applications, and it makes no difference. This has happened at both 44100 and 48000 sample rates.

Do you have a MIDI keyboard? Is it possible that it is sending pitch bend data? (Some M-Audio keyboard had problems with knobs sending data all the time, IIRC.)
I don’t think I’ve heard any other posts about Dorico doing anything like this, apart from the usual sample rate mismatch, but that affects everything.

spencered, I am a victim of the same behaviour.
It happens with one oboe or one of the violins in a string setup, or with one of two clarinets. They will become out of tune by one half note even, just randomly. I normally stop playback (as it becomes unbearable) and restart playback. Sometimes I am lucky and those instruments start at the right pitch again, sometimes not. I can sort of work against it by turning the pitch bend wheel of my MIDI keyboard.
I promised myself to dismantle the keyboard and clean its inside of any dust. The two wheels seem to work optically, so dust might be the culprit:

Turning my keyboard off before playback seems to solve the problem for me.

How are you starting playback? Do you use the floating palette and the option to start from selected? I ask because I think that a hardware controller signal would only be sent to the currently highlighted track. If so, a solution would be to ensure that the hardware isn’t linked to a specific track before beginning playback.

Thanks for the good suggestions, everybody. I can unplug the iRig keys and see if it goes away.