Drupal 8 Ajax Form Submit works only once?
Your problem is probably here:

$form['submit']['#value'] = time();


You are changing the value of the submit button in the ajax callback. However, Drupal has already cached the form before the Ajax callback is hit. Why that matters is that Drupal uses the value of the submit button to determine which button was clicked, comparing it to the values in the cache. Since your cached value will be different than the submitted value, it cannot properly determine what it needs to do.

You need to change the value of the submit button either in the form definition, or in a form_alter hook.