It sounds like a sys-ex message to turn a drum track into a normal track. Then , if the PC# got sent before the sys-ex, keyboard is likely to play Piano (#1) as a default sound.

Can you copy the sys-ex message and post it here (should be fairly short)?

Perhaps I can take a look at it and see what is going on...
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An arranger is just a tool. What matters is what you build with it..!