Under the hood, get_dirsize() uses recurse_dirsize() which uses a transient called dirsize_cache. Try clearing that transient and check again.
To do so, you can use one of the following methods:
- call
delete_transient('dirsize_cache'); - use WP CLI’s
wp transient delete - use a plugin
Looking further through the source code, I think it should be possible to use recurse_dirsize() directly in your code and telling it not to cache like so:
$upload_dir = wp_upload_dir();
$size = recurse_dirsize($upload_dir['basedir'], null, null, []);
By passing an empty array [] as the fourth argument, it should circumvent the cache because the !isset($directory_cache) now returns a different result.