Maybe someone can check if there are any MIDI CC events that are forcing a specific MIDI channel. Sometimes that can cause issues until you remove the particular event.
I've been through the step-edit dialogue and set everything to the same channel and it's made no obvious difference. An oddity still is that that process shows everything now on channel 6, though other people here believe BIAB has it on channel 3. I'm not doubting what anyone says, just puzzled why the channel seems to be different in different places.
FWIW, the first two notes in the step-edit and a number of rests were on channel 1. Everything else there is on channel 6. How it gets to channel 3 I know not.