VHorns Brass Section not present in exported files

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Hi all.

I'm using Brass Section in Reaper through the UVI Workstation plugin. I can hear the sounds on playback, and can see the audio signal on both their own tracks and the master faders, but when I render the project it creates a track with all other instruments except brass section (other midi instrument tracks work, like Superior Drummer).

I did notice one instance of a render where all the Brass Section sounds were muted aside from the the last note for some reason?

I've checked the settings in the plugin and can't see anything obviously wrong (the send is being sent to the master bus, etc.) - has anybody had this problem and found a solution?