I'm marking this a support request because I can't believe its a bug which hasn't been reported. Nonetheless:
In Drupal\views\Plugin\views\argument\Date:

  public function defaultArgumentForm(&$form, FormStateInterface $form_state) {
    $form['default_argument_type']['#options'] += array('date' => $this->t('Current date ....'));

Seems to imply that there is a default_argument plugin called 'date' But when I select that plugin I get an error and I can't find any such plugin in drupal core.

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matslats created an issue. See original summary.

matslats’s picture

matslats CreditAttribution: matslats as a volunteer commented
Title: Can't find iews default_argument 'date' » Can't find views default_argument 'date'
dawehner’s picture

dawehner
Primary language German
CreditAttribution: dawehner as a volunteer and at Chapter Three commented
Status: Active » Fixed

#2325899: UI fatal caused by views argument handlers no longer can provide their own default argument handling this is the bug for that particular problem.

Status: Fixed » Closed (fixed)

Automatically closed - issue fixed for 2 weeks with no activity.