Tuning problem/split pitch HELP please

[Giner]

Hi. Playing my Pa3x-61 in full keyboard mode everything is as it should be.

However, putting it into 'split' mode (my go-to split point is A2), there is a change in pitch from the left side to the right side of the split point. As far as my ear can tell the right hand side is flat by about a semitone compared to the left side, which stays on pitch. Any suggestions, please?

I should add that this throws the harmoniser off, too. It's as if the harmoniser can't decide which side of the keyboard to generate harmonies from.