Only exporting the audio of one instrument from my Dorico Project

Hi I have a sonata for flugelhorn and piano that I am writing and I wanted to export the audio. I am using note performer with dorico 5. My sonata has 3 flows, I go to export the audio as separate files for each flow and the first flow only plays the flugelhorn audio and not the piano. The other two flows come out perfectly. Does anyone have any potential solutions?

You could send me the project file to u dot stoermer at steinberg dot de and I could have a look. Full confidentiality guaranteed from me.