How you are loading the json does not matter. acf/load_field_group is called after every field group is loaded.
I don’t know anything about $GLOBALS['post_type'] Is this set at the point that you are checking it? I don’t know, but I am going to assume that it isn’t and you’re probably going to need to find another way to determine the post type.
function toind_get_flexible_content( $field_group ) {
var_dump($GLOBALS['post_type']);
.................................
