I gave it another go and the script I posted works flawlessly. Used AddUnique instead and added an element to the FinalArray just to replicate your workflow.
What is the duplicate that you’re seeing?
Here’s a log; 9 iterations and the final array contains 9 elements, all unique, and the initial element 0 is also accounted for. Each iteration adds something unique at the end.
Here’s how I print the content:
