MIDI channels broken

Ok this is immensely frustrating. Simple scenario:

I created one MIDI port in LoopBe30 (windows 10)
Disable the port in Dorico Preferences MIDI input devices to avoid feedback
Set channels 1-16 in PLAY for my first 16 players
In Cubase I add 16 MIDI channels 1-16 and route their output to HALION rack instrument
In Halion I have 16 instruments, channels 1-16

I should get 16 independent parts, right? Wrong, every instrument is playing every part, total chaos!! Am I doing something incredibly wrong or the MIDI output channels in Dorico are broken? I know they can play independently with Vienna but why this mess when I use a simple MIDI port that should send 16 individual channels out?

Just updated to Dorico 4 and very frustrated that something this simple isn’t working.