Duo Mix playlist isn't working

[YoliiiXO]

Plan

Premium Duo

Country

Dominican Republic 

Device 

Samsung Galaxy S7 

Operating System

Android Oreo

My Question or Issue

My boyfriend and I have had the Premium Duo for 3 weeks now, and in our Duo Mix there are no songs by the other (In my playlist only my songs appear and in his only his)

How do we fix this?

(I left a screenshot so you can see what I'm talking about)