Roland SPD SX -> Rytm - skipping notes every now and then

[Stoss]

I experienced the exact same thing as you. I talked with support and they have yet to correct the problem. On the forum I worked with others to get a functioning work around.

Have a read through this:

Using External Drum Pads as Trigger for AR

Good to hear that it works now. Maybe you have to adjust the trigger threshold or the pad sensitivity a little bit.