Had the same issue... Bought all the instruments expecting to get them to play together when I zoned in only to be seriously disappointed. I posted this on the bug forums and it was moved into the not a bug section immediately, also had contacted help desk and they were (as usual) unhelpful.

Looking at a video of these instruments from a previous patch it seems like they changed the sound of the timpani, I am wondering if that had something to do with messing up the auto play?

Either way, seriously disappointed and hope they rectify this.