I don’t know if it’s a bug but when my soprano plays, the mixer indicates that it’s the alto playing and vice versa, when my alto plays the mixer indicates that it’s the soprano playing.
@Ibadez38 , have a look at the mixer in Kontakt, there the Alto is on channel 3/4 and not 5/6. So there is the turn, not on Dorico side. Dorico’s mixer follows the channel names of Kontakt.