When I disable Natural Arrangements in Song Settings, the electric piano played E5 for me.
I also tried the progression "C5 - - Eb5 - C5 G5 - F5 - Eb5" that you mentioned with the Song Settings adjusted, the electric piano played fine.
When I had Natural Arrangements set to either "Enabled" or "As set in arrangement options", major chords were generated.


MY SONGS...
Audiophile BIAB 2025