The INSTRUMENT 1 uses pitch bend, a type of MIDI control, to get seamless fretless sliding. In order to allow these techniques to work with third-party sound generators, the INSTRUMENT 1 sends pitch bend data on multiple MIDI channels.
Some music apps do not allow for multiple MIDI channels with pitch bend. In this case, set the INSTRUMENT 1 to Single Channel MIDI mode using the iOS app or the Mac/PC Preset Editor.
This mode allows notes to play on only one channel. Only one note at a time can be played in this mode, sliding up and down the fingerboard with the correct fretless behavior.
The Artiphon App and INSTRUMENT 1 Editor allow you to change the Pitch Bend Range output of the INSTRUMENT 1 to 12, 24, or 48. The external synth or virtual instrument needs to match that setting for Fretless mode or Pitch Bend to work correctly.