is it possible that the inner arrays are just None and you need to create arrays there first?
i don’t even know how to make empty arrays dynamically, seems Make Array takes the type of the array from the items you put in. 
edit: apparently to create arrays, could just make a function with an array as a local variable and return that.
if you care about using a blueprint solution, could also just “flatten” your data into a one-dimensional array.