You need to capture the current ID outside of the loop, otherwise get_the_id()
will grab the ID of the post it is currently querying.
Try moving that chunk of code before the while
, e.g.:
<?php
if ( is_singular( 'playlists' ) ):
$current_category = get_field( 'categorias', get_the_ID() );
if ( have_posts() ):
?>