That error indicates that you have a type unstable construction of an object, which contains both type unstable non-differentiated data and type unstable differentiated data.
We specifically do not support that yet, so we throw an error rather than risking an incorrect answer.
On 1.10+ you should get a nicer backtrace showing fully the context of where it’s happening.
Perhaps update that area of the code to be type stable (which regardless would be good for performance too)?