Ran into an issue in no signal where Godot was loading Vector2i values as String values. As it turns out, this is because Godot's JSON implementation does not round trip correctly:

extends Node

func _ready() -> void:
	var value: Vector2i = Vector2i(3,2)
	var string = JSON.stringify(value)
	print("String: ", string)

	var parsed = JSON.parse_string(string)
	print("Value: ", parsed)
	print("Value is String? ", parsed is String)
	print("Value is Vector2i? ", parsed is Vector2i)

The above code outputs:

String: "(3, 2)"
Value: (3, 2)
Value is String? true
Value is Vector2i? false

As you can see, Godot converts the Vector2i to a JSON string without any type information, so it can only reasonably parse the JSON string as a String when parse_string is called.

Instead, I was able to get around this issue by using var_to_str and str_to_var instead of the JSON API.