Stripe processor: payment going through but registration is not! "Could not find valid value for id"
That looks like a bug in the events component (possibly, specific to Joomla). The error is happening in the constructor of an object that is managing the event registration process (https://github.com/civicrm/civicrm-core/blob/master/CRM/Event/StateMachine/Registration.php), presumably after the payment has occurred. It's failing to get the id of the event, which it normally will pick up from the url or as a hidden post value from a form.

The numbering of the error line suggests that your CiviCRM version is not up to date, and I suspect you're using the event "cart" feature which is not as maintained as the standard event form/flow.

Conclusion: probably not stripe related, but a CiviEvent error.

Also, here's a similar post: CiviEvent: Could not find valid value for id (Drupal 7.6.1)