Odd MIDI behaviour

Having got up and crawling, if not running, with GA4 I have a weird issue that is perplexing me as I cannot find the solution.

My hardware is an Akai MPC (Elements version) and a Novation Impulse 61. I have the latest drivers for both installed.

The issue is this with MIDI control set to all MIDI inputs:
Groove Agent stand alone: doesn’t respond to Impulse, MIDI activity indicator comes on for the MPC, but nothing is triggered (pads are mapped correctly) and ‘edit/learn trigger note’ is greyed out.
Groove Agent in Reaper: Impulse works, MPC midi signals are seen by Reaper (and works with Addictive Drums), GA learns trigger notes but is not triggered.
Cubase Artist 9: Everything works.

https://www.youtube.com/watch?v=Qz2Rli5ZKl0

The obvious answer is only to use Cubase, but alas the project I am working on with some friends is being done in Reaper . . and it would be quite useful to have the stand alone version work too.

Pleased to report that I have solved part of the problem. Now working with the MPC in Reaper - although I still can’t get the stand alone version to respond to anything.
The trick was to change the MIDI channel inside of GA to match the default channel from the MPC, 10 in this case.