I strongly believe that your issue is different to the one drewt4 has, therefore I kindly ask you to open a new thread instead.
Further question, is it broken only in Dorico 3 or was it already in Dorico 2 a problem?
Also, does it happen with any project? What if you creat a simple piano project and try to connect that to Logic/Kontakt?
I expect the problem is that the new MIDI output you’ve configured to send MIDI to Logic is also being used as an input in Dorico. creating a MIDI feedback loop. Go to the Play page of Preferences and click ‘MIDI Input Devices’, and make sure the IAC Bus you’re using to send MIDI out to Logic is not enabled as an input device.
The same project file (produced in Dorico 3) works in Dorico 2 without problems.
Logic plays the notes on the staff when playing the Dorico project by pressing p.
Kontakt plays the notes on the staff when playing the Dorico project by pressing p.
Logic and Kontakt play a note by selecting it in Write mode correctly.
GUI responds as expected by clicking the mouse button only one time.
Dorico 3 shows the same phenomena with a new simple piano project:
Logic plays the notes on the staff only when playing the Dorico project by pressing p.
Kontakt does not play the notes on the staff when playing the Dorico project by pressing p.
Logic and Kontakt do not play a note by selecting it in Write mode.
GUI does not respond as expected… I should press the mouse button repeatedly quickly.
I already checked it. In my project, there is no MIDI loop between applications. If there were a problem of MIDI loop, the same project file might not work in Dorico 2. However, the same project file works in Dorico 2 without such problems.