I've got the latest mGB (1.3.3) flashed onto a nanoloop cartridge in a DMG-01 Gameboy, and using the nanoloop USB I've got it accepting MIDI. Playing on channels 1, 2 or 4 is absolutely fine and pretty much as expected. If I send anything to channel 3 (or 5) mGB very quickly crashes, hanging on the last note played and garbling the screen.
Has anyone else had this? Any ideas what has gone wrong? Have I done something monumentally stupid?