godot 4.1 tilemap updates not working as expected?

gamemanager.gd

func create_warren(location : Vector2):
	var local_pos = tile_map.local_to_map(location)
	var tileset_source_id = 6
	var atlas_coords = Vector2i(0, 0)
	var buildings_layer = 5
	
  # add building to tilemap
	tile_map.set_cell(buildings_layer, local_pos, tileset_source_id, atlas_coords)
	
	var ground_layer = 0
	var building_layer = 5
	var tile_data : TileData = tile_map.get_cell_tile_data(ground_layer, local_pos)

	# set has_building for every tile the building touches
	var i = -5
	while i < 5:
		var l = local_pos
		l.x += i
		print(str(l))
		var next_tile_data : TileData = tile_map.get_cell_tile_data(ground_layer, l)
		if next_tile_data:
			tile_map.add_modulated_cell(l)
			# trigger TileMap._tile_data_runtime_update
			next_tile_data.set_custom_data(tile_has_building, true)
		i += 1

tilemap.gd

extends TileMap

var modulated_cells : Dictionary

func add_modulated_cell(v : Vector2i):
	modulated_cells[v] = Color.DARK_RED

func _ready():
	pass
	
func _use_tile_data_runtime_update(layer, coords):
	var r = modulated_cells.has(coords)
	return r
	

func _tile_data_runtime_update(layer, coords, tile_data):
	if layer == 1:
		var color = modulated_cells.get(coords)
		tile_data.modulate = color
		force_update(0) # removes my layer 0 while also modulating somehow
		print_debug(str(tile_data.get_custom_data("has_building"))) # returns false somehow