For starters, you had better make sure that the Yamaha is set to only receive on the one channel. If it is playing both sides even when split, that is somewhat unusual, as Roland definitely tend to set up arrangers so that each part sends on a different channel.

I have a strong feeling that this issue has more to do with the Yamaha than the Roland, but I could be wrong… It DID happen that one time! LOL 😂

Happy Thanksgiving, Cassp… 🦃