The %element-title is using the following invalid tokens
It seems that in order to nest those tokens a "dummy" token is needed that matches group name:

function MY_MODULE_token_info() {
  $tokens = array();
  $types = array();

  $types['master'] = array(
    'name' =&gt; 'Master group',
    'description' =&gt; 'This is the master group',
  );

  // This is needed in order to nest tokens:
  // a dummy token that is the same as nested group/type
  $tokens['master']['sub_group_1'] = array(
    'name' =&gt; 'Sub group 1',
    'description' =&gt; '1st tokens group',
    'type' =&gt; 'sub_group_1',
  );

  $types['sub_group_1'] = array(
    'name' =&gt; 'Sub group 1',
    'description' =&gt; 'This is the first sub group',
    // this tells this group that it's parent is 'master' group.
    'needs-data' =&gt; 'master',
  );

  $tokens['sub_group_1']['token_A'] = array(
    'name' =&gt; 'Token A',
    'description' =&gt; 'This token prints letter A',
  );

  return array(
    'types' =&gt; $types,
    'tokens' =&gt; $tokens,
  );
}