Hi same thing appears to be happening with me. Just bought keystep pro, updated to the latest firmware. So far so good, hooked KSP up to my synths (o-coast,sub37,Westpest, drums). Midi settings as expected. the o-coast will control fine then just disappear, I check the midi setting and nothing has changed, just kinda drops out. The sub37 has been fine with no issue and the west pest will not receive at all.
I tried moving things around midi channel wise but nothing helps, it seems if I do a factory reset then the 0-coast will be controlled again for some time, then drops out (again no changes to midi settings just factory reset)
* I have only had the KSP for a few days, I am coming to KSP after having a keystep and beatstep pro so I am fairly familiar with Arturia equipment but never ran into this type of issue.
I know if I was reading this post I would think set up issue. but I have triple checked and all is as it should be. I'd appreciate any help with this if anyone else has encountered it