Im having this code
$concours_termine_cat = get_term_by('slug' , 'concours-termine' , 'product_cat');
get_term_by is returning false, after debugging the get_term_by function
taxonomy_exists( 'product_cat');
is returning false.
So I checked in taxonomy_exists function and looks like into $wp_taxonomies
product_cat doesn't exist at this time of execution.
I call this hook like this add_action('transition_post_status' , 'vince_function_post_update' , 10 , 3);