mrcc880 no midi f/ Keystep 37

[unkleelephant]

New owner of an MRCC 880 here. I'm pretty new to MIDI workflows and I can't the get the MRCC 880 to receive Midi note data from my Keystep 37. It receives and sends data from my Roli Seaboard Block M just fine, but nothing registers from the Keystep. I know the Keystep is sending midi data, as indicated both from Ableton and from Arturia's midi control center. I've double checked the 5-pin din cable and it works fine when sending midi out of the Keystep directly into my desktop Hydrasynth. However, when I try and route through the MRCC 880, I get nothing.

Can anyone shed some light on why these two devices aren't communicating?

Big thanks in advance for anyone willing to assist,

Stephen