Groove Agent won't trigger from Keystep Pro

I have CB12 and GA5. Both work fine and as expected. I have a new Keystep Pro, which seems to work fine with stand alone VST’s, external hardware, and with VST instruments inside Cubase, except for 1 problem. I know how to set up the Midi channels on the Keystep and Cubase to get the synths to trigger correctly via the Keystep keyboard and the sequencers etc BUT I cant get GA to trigger from the Keystep no matter how I tried. I’ve set both GA and the keystep to every midi channel and also the “all” midi channel. I have tried using the input transformer to pass only the drum (10) channel as it is set to the default output channel on the Keystep drum track, but I get no response.Cubase is certainly receiving midi from the Keystep drum track because the Midi receiving indicator at the bottom right of the main window shows the Midi notes coming in. If I set other Keystep tracks to other synths and midi tracks it works perfectly, but with GA, I get nothing.
The Keystep works fine with its default drum track settings with external hardware, right out of the box.
Any ideas what I am doing wrong?
Thanks for reading.