Maybe the MIDI track is sending program changes to the instrument. You could try to remove them or filter them out. I Have never used them and can’t give much detail but check the MIDI track at the bottom where the controller lanes are. Select the “Program Change” lane and see if there is data there.
HTH
J.L.
Just looked at HALion Sonic. On the Options page, there is a Global “Program Chage” setting. Maybe you have in on General MIDI? Try putting it to “Off”.