Not sure about implementation under the hood of the arrays, so… Can Add() and/or AddUnique() change the order of elements in array? Like if we reach some magic number and memory needs to be reshuffled, etc. If it’s an actual array then it shouldn’t but maybe it’s a dynamic array or a mix of array/list… Can’t find any info on that anywhere, documentation has no info…
I assume they don’t.
If you want to be sure, just install VS and double click the node… 
Add & Add Unique do not.
Remove does via shifting.
e.g. Index 0-99, remove 0 and the array shifts. 1 → 0, 2 → 1 etc.