Can you guy tell me why?

Yes. When setting up the Note Limits, you only set up one set of Note Limits, and likely neglected to setup the other. I’ll explain...

The two set of parameters to deal with are:
1) Part Note Limit range — appears on the main HOME screen. These determine in what Range the instrument in the Part will sound.
2) Arp Note Limit range — appears on the Part Edit > “Arpeggio” > “Common” screen. These determine in what Range the keyboard will control the Arpeggio Phrase.

Yes they can be different. You probably don’t want the right hand (Piano) controlling, sending instructions to the guitar or vice versa. A quick adjustment to the Arp Note Limits will do the trick.
_ Set the Arp Note Limits for the guitar in Part 1 so that it only receives instructions from the lower region of the keyboard. You want the guitar to *sound* across the keyboard, but only the lower region to *control* it.
_ Set the Arp Note Limits for the Piano in Part 2 so that it only receives instructions from the upper region of the keyboard. You probably want the piano to “sound” across all keys, but only the “control” in the right hand. Make sense?

Call up your Performance
Press [PART SELECT 1]
Press [EDIT]
Touch “Arpeggio” > “Common”
Find the Arp “Note Limit” and set it accordingly... the range on the keyboard that you wish to feed information to th guitar Arp Phrases.
Rinse and repeat for the piano in Part 2, setting the key region to control the piano Arp Phrases.

[STORE] your Performance.

Extra Credit: notice the “Octave Shift” parameter... this allows you to offset the results of your controlling key presses.... in case the instrument you’re controlling doesn’t match the keys you are using to trigger it.
When YOU press a key on the keyboard, playing the instrument normally, the Note Limits for the Part determine the split. However, when the Arp is “playing” the instrument, it has to interpret your key-presses, then output the appropriate note-on messages to the tone generator... and because the output of the Arpeggiator can be in a different range than the notes you trigger, these two separate Note Limits must exist.

Hope that helps.