Is it "part full" or "memory full"?

https://yamahasynth.com/ask-a-question/memory-full-1

You may want to turn aftertouch receive off when recording to prevent filling up the recorder with unnecessary aftertouch events.

Although for Montage - it applies to MODX as well:
https://yamahasynth.com/learn/montage/mastering-montage-pattern-workflow-and-recording-features-in-os-v3-5

Search for "aftertouch" and you'll find how to erase aftertouch events from recorded patterns.

Relevant section:

There may be instances where you want to erase a certain controller from a track but not the entire track. For example, if you recorded a track with a lot of aftertouch that you want to get rid of, but you like the track itself, you can use this job to delete only aftertouch and nothing else. This feature is now available on in OS v3.5 under [Edit/Job]>[Song/Event]>[Erase Event]:

... and choose "Event Type" as "Aftertouch".

Not sure what is wrong with my MODX, but when I push the button to add a rythm pattern, I get an error "part full".

I started a performance from scratch; filled all 16 parts with single parts, and everything is fine if I select each part individually; so the performance should be fine.
Although I want to add arp to 4-5 parts to play them one at time, but I can't get this done. Is this a bug? To my knowledge, a rhythm pattern is not taking a part, but using whatever you have selected, so I don't get why I get the "part full" error.

When you have occupied all 16 Parts you cannot add a Rhythm Pattern via the dedicated button.

You are misinformed about about the Rhythm Pattern not taking a Part — Of course it does.

Forget for a minute, your (already filled) 16 Part Performance. What follows will serve as a quick tutorial that will explain how the [RHYTHM PATTERN] button is intended to work. And we’ll explain why it is completely inappropriate for your situation.

Let’s call up “CFX Concert” — this is a four Part Performance.
Say you are messing around trying out some compositional ideas, and you wish to quickly add a Drum groove.

From the HOME screen:
Press [RHYTHM PATTERN]
A special “Category Search” screen appears that will allow you to select a Drum Kit for the first available (empty) KBD CTRL Part. Each Kit will have several Arp Phrases pre-assigned.

Here’s how that works:
You pick from among the Drum Kits. If you pick a Rock Kit, expect a rock drum groove, select a Jazz Kit, expect a jazz swing groove, select a Hip Hop Kit expect a Hip Hop groove, and so on. This is for speed. By selecting a Kit, it will automatically be added to the first available Part... in this example, that is Part 5.

Of course, you can change everything.
When you select a Kit... use the “Page” box to view more Kits....

You need only choose the Kit by tapping its name, the “Rhythm Pattern” function does the rest, automatically.
It will:
_ Assign five or more Drum Arp Phrases... selectable right on this screen. Arp 1-8
_ Set “Arp On/Off” to On
_ Set “Arp Hold” to On
_ Set “Arp Play Only” to On (if you press ARP STOP, the Drums will not play along with the Rhodes — the drums will only sound in response to the Arpeggiator. Why? Because Drums layered with Rhodes just sound silly! lol.

All these things you would have to do manually. When you quickly want to call up a Drum groove to play along with... this is speedy and efficient. You call up a Rhodes, you want a pop groove... press [RHYTHM PATTERN], you tap “Real Drums1” and start jammin’... just as quick as that!!!

On this same screen, you can adjust Tempo, Volume, even change the Arp Phrase assigned to any of the 8 Arp Select screen buttons. You just touch a key to start playback.

If you have filled all eight of the possible KBD CTRL Parts, 1-8, then you CANNOT *add* a Rhythm Pattern using this feature. That’s why you are getting the “Part Full!” Error message... you do not have a KBD CTRL Part available (1-8).

Here is a short tutorial:
Mastering MODX: Rhythm Pattern

Extra Credit:
Often you may use the on-board Arp Drum grooves for inspiration — better than a click — you can remove them later, redo them, etc.
You can go to the Sequencer and lay down your idea... each item records to its own Track. You redo the drums later.