Thanks for the detailed bug report, that’s really odd!
Since 4 channels are recognized, it means that iOS reported 4 channels to Music Studio and Music Studio is probably receiving on 4 channels.
What I can’t explain is why channels 3+4 are silent. Please try the following:
- Unplug all hardware and quit all apps
- Restart your iPhone (hold the power and the home buttons for 10-20s until the Apple logo appears)
- Plugin the UR242
- Launch Audiobus first
- Then launch Music Studio
- Check if inputs 3+4 receive a signal