keesiemeijer on "WP_query and MySQL lost connection"

Try it with this [untested]:

$query_array = array('relation' => 'OR');
    array_push($query_array,
    array(
      'key' => 'filter1',
      'value' => array('value1', 'value2', 'value3'),
      'compare' => 'IN'
    )
  );

https://codex.wordpress.org/Function_Reference/WP_Query#Custom_Field_Parameters

Do you still get the error?