via: https://cnpagency.com/blog/the-right-way-to-do-wordpress-custom-taxonomy-rewrites/
I needed to change the order of registering the taxonomy (make sure it’s before CPT) and the CPT (make sure it’s after registering any taxonomy).
Now
'rewrite' => array( 'slug' => 'resources/tags', 'with_front' => false ),
works as expected!