Sorry for the slow reply. I think a code line associating tags with attachments got wiped out by the upgrade.
register_taxonomy_for_object_type( 'post_tag', 'attachment' );
It should be called from a callback hooked to “init” action. The code probably disappeared because it was not put in a safe place. The only safe places for custom code is your own site specific plugin or a child theme.
Apologies if none of that makes any sense to you. I can explain further, but didn’t want to waste time explaining if you already understand with just that.
Where would I go into to change the code to above?
There’s more to the required code than what I first posted, you need the callback code for the “init” action. Like this:
add_action('init', function() {
register_taxonomy_for_object_type( 'post_tag', 'attachment' );
});
To keep this code from disappearing again, it should go in functions.php of a child theme or the main plugin file of your own custom plugin. Neither one is that difficult to create. A plugin is slightly easier. Naturally you must activate which ever entity you create. Any other custom code you may need in the future can go into this same entity.
