Others have also reported issues with the external instrument plug-in. Works in Logic, but not in MainStage. An alternative is to configure an external midi instrument on a channel strip. A midi instrument can send program change commands for bank and patch. It works.
Lastly, some external synths require that you turn local control “off” on the global config. This is the case with my Roland XP-30. If local control is “on” the synth engine will only accept midi CC commands from the synth keyboard.
Logic 10.6.1 / MacOS Catalina 10.15.7 / Mid-2014 MacBook Pro 15” w 16GB RAM, 1TB SSD
Novation LaunchKey 49 MK3/ Novation LaunchPad X / FaderPort 16
UA Apollo Twin X / MOTU Traveler & 8Pre/ Adam T7V pair/ Inspiration