If you click the midi plug icon bottom left of screen it will open the midi monitor.

Watch and see if it's adding to the data and has a problem.

It shouldn't be generating anything other than midi clock maybe.

You created a controller device?

Is it set to be a HUI device internally?

I used to run one a couple years ago. I think I preferred the MCU Sonar mode on the unit.
In Studio One, you would add US-2400 Port 1,2,3 as MCU, MCU extender, MCU extender respectively. I think Port 4 was Transport controls and Port 5 was the Joystick.

On the bottom of the external devices page, there is a button for "Placement". Use this to combine your 3 MCU devices into one controller.

Thanks for the replies. mycbeats - I tried you suggestions. I did end up having to use one MCU and four extenders. I put the MCU and the first two extenders in group 1, the fourth extender in group 2 and, the fifth extender in group 3. Most things are working but, a few things are not. It is not spitting out continuous breath controller data like before. I will try some different configurations tomorrow.

Well, I've got pretty much everything that I personally need working. One thing I cannot get to work is making S1 display the selected track when I touch a fader. I suppose I can live without that feature but, it would be nice if it worked. (Note : This does work in Cakewalk but not in S1)

Highlighting a track in Studio One just by touching a fader on the control surface is not a function of Studio One. No matter which control surface you're using. So you're not missing out on anything.