Official comment
It's possible that because they're velocity-sensitive pads that the hardware isn't transmitting a value high enough for the software to register the "change." For example, the midi range is 0 to 127. If the software only recognizes a press when the value is at 127, but pressing the pad softly only sends a 30, you've not met the 127 required for the trigger.
My recommendation is to try and change it to non-velocity-sensitive, or see if KORG has a tool allowing you to change the output type, or your last option would be to use a MIDI software capable of translating any press on that pad to a different value (127).
