Each keyboard has an ID string so the system knows what it is. I'm wondering if the new keyboard is from the older 2015 model.
Also which keyboard did you get a US standard or one of the foreign language ones?
In either case go into About this Mac > System Report, then open the Hardware tab and jump down to USB. On the right panel open the twistys under USB 2.0 Bus > Hub and click on the Apple Internal Keyboard / Trackpad. Now copy off the lower pane's info and paste it here.
I don't have access to your exact model hopefully someone else does so we can get a comparison to see whats different.