@greg_smith Iām not sure why, but tried again on Revit and I could replicate the issue. For some reason Dynamo Sandbox works just find but is Revit messing up things (not surprise there though).
I downgraded the Newtonsoft.Json I was using to 9.0.1 (same as Revit). and the duplication disappeared. I have updated it on the Package Manager to version 2.0.2 so please give it a try and let me know if this solves the problem once and for all 