First, you can make sure that your variable isn’t getting re-assigned by accident. This is as simple as assigning the array into a global variable and checking that (your_array == global.also_your_array).
If it’s not that, you can use function hooking to check for your array being modified in the few functions that can reduce array length (I think that’s just array_resize and array_delete..?)
I’ve also seen some bizarre things happen after calling Steamworks functions that accept arrays of strings (mostly the workshop item tag function, I think).