Error in InlineEntityFormSimple::isDeleteTriggered()

In some circumstances I'm receiving:

TypeError: in_array(): Argument #2 ($haystack) must be of type array, string given in in_array() (line 185 of modules/contrib/inline_entity_form/src/Plugin/Field/FieldWidget/InlineEntityFormSimple.php). Drupal\inline_entity_form\Plugin\Field\FieldWidget\InlineEntityFormSimple->isDeleteTriggered() (Line: 141)
Drupal\inline_entity_form\Plugin\Field\FieldWidget\InlineEntityFormSimple->formMultipleElements() (Line: 120)
Drupal\Core\Field\WidgetBase->form() (Line: 616)
...

This happens in InlineEntityFormSimple::isDeleteTriggered():

  protected function isDeleteTriggered(FormStateInterface $form_state): bool {
    $triggering_element = $form_state->getTriggeringElement();
    return isset($triggering_element['#submit'][0]) &&
         in_array('deleteSubmit', $triggering_element['#submit'][0]);
  }

When I inspect $triggering_element['#submit'][0], I'm getting inline_entity_form_open_form.