Find doesnt work in loaded data from disk?

Godot 4.3

I cannot get find, has, in work in my project when using data loaded from disk?
In this case for loop works, but there must be something I clearly have missed? :face_with_peeking_eye:
code below:

func check_is_already_given(
	reward : B_RoadReward, 	data, 	cup_id : String, index:int
	)->bool:
	var check := false
	var res : Array = data[cup_id]
	var test := [1,2,3,4]
	printt("res find",res.find(index))
	printt("test find",test.find(index))
	printt("res",res,"test",test)
	for x in range(res.size()):	
		if res[x] == index: check = true; break
	#could not get find, in, has etc work in this ????
	if check:
		print("FOUND ",check);
		return true
	return false

printed output:

res find -1
test find 0
res [1, 2, 3, 4] test [1, 2, 3, 4]
FOUND true
res find -1
test find 1
res [1, 2, 3, 4] test [1, 2, 3, 4]
FOUND true
res find -1
test find 2
res [1, 2, 3, 4] test [1, 2, 3, 4]
FOUND true
res find -1
test find 3
res [1, 2, 3, 4] test [1, 2, 3, 4]
FOUND true