I mainly use Scaler with a midi controller. When I set up Scaler 3 as an AUv3 or standalone I can only get my Divisi tracks to trigger with the main play control not by the section C play button or midi binding. It was so simple in Scaler 2 as you just set it to multiple channels midi out put and it worked with midi binding. Frustrated a I spent many hours trying to figure things out. Most YouTube stuff is about the computer version and not iOS AUv3.
I understand what you formally called multi channel out is now referred to as Divisi. You moved it from settings to the arranger and made it more complex as you now can host in the stand alone. There is no mixer in the AUv3 as the host does that. Midi binding should work like it does in Scaler 2 but unless I missed a step, it doesn’t.
Only the Main track band be bound but not the Divisi tracks.