Seems like your FO initially thought you were a 2015 selectee, hence the promptly scheduled interview in Sept before the start of your applicable FY. The petition then got denied after the interview once they realized you're a 2016 selectee. Does your online status indicate the approval date? Has it shown any update regarding card production being ordered? You should call the USCIS customer service number to follow up on your case - request to speak with a Tier 2 officer after politely listening to the customer service rep read out exactly what you've already seen online when you checked the case status yourself.
This is what I got when I check my status "On December 15, 2015, we approved your Form I-485, Application to Register Permanent Residence or to Adjust Status, Receipt Number MSCxxxxxxxxx. We will mail your approval notice. Please follow the instructions in the notice..."
I was surprised that an interview was scheduled so fast when I first filed, it seems so that this was the reason. I'll contact USCIS customer service tomorrow as you advised to follow up.
Thank you Sm1smom!