index.php

<?php $categorias = ["alfa", "beta"];
$args = [
  'post_type' => 'post',
  'posts_per_page' => -1,
  'orderby' => 'rand',
  'tax_query' => [
    'relation' => 'AND',
    [
      'taxonomy' => 'grupo',
      'terms' => ['alfa', 'beta'],
      'field' => 'slug',
      'operator' => 'AND'
    ],
    [
      'taxonomy' => 'category',
      'field' => 'slug',
      'terms' => 'premium'
    ]
  ]
];

unset($args['tax_query'][0]['terms'][1]);

if (is_user_logged_in()) {
  $user = wp_get_current_user();
  $args["author"] = $user->ID;
  unset($args["post_status"]); ?>
  <h1>Publicaciones de <?php echo $user->display_name; ?></h1>
<?php } else { ?>
  <h1>Todas las publicaciones</h1>
<?php }

echo  '<pre>'.print_r($args, 1).'</pre>';
$entradas = new WP_Query($args);
//echo '<pre>'.print_r($entradas->query_vars, 1).'</pre>';
if ($entradas->have_posts()) {
  $c = 0;
  while ($entradas->have_posts()) { $entradas->the_post();
    $c++;
    echo $c.': '.get_the_title();
    echo '<hr>';
  } wp_reset_postdata();

} else {
  echo '<p>No se encontraron artículos</p>';
}