https://support.stagetraxx.com/d/4778-how-to-write-a-good-forum-post
It would help if you provided more and clearer detail. You should assume no-one knows anything about the Soundcraft UI24R when describing what you are doing. By leaving out all detail you are really relying on another ST4 user that has had experience with that specific mixer maybe knowing what you are talking about.
I assign the usb channels within the UI app for playback
What "UI app" are you talking about?
The Stagetraxx app recognizes the UI
What do you mean "recognizes the UI"?
Etc etc.