A reminder email with {action.*} tokens blocks delivery for itself as well as subsequently processed reminders

Inclusion of the tokens {action.unsubscribeUrl} or {action.optOutUrl} (or possibly other {action.*} tokens) in a reminder email causes the email to fail to be sent to the recipient.

Furthermore, any other reminders that are subsequently processed in the job.send_reminder API call will also fail to be sent!

The problem persists even after the expiration of the offending event. To resolve the problem, it is necessary to disable the reminder on the offending event, or remove the offending token.

The failure is largely silent, with no log entries in the CiviCRM log file or in the Drupal log. The failure is, however, visible in the scheduled job log for Send Scheduled Reminders:

Finished execution of Send Scheduled Reminders with result: Failure, Error message: Error: Cannot use action tokens unless context defines mailingJobId and mailingActionTarget.

There is, unfortunately, no indication in that message of which reminder caused the failure, leaving the Admin to search through all enabled reminders.

Background info:

The offending reminder (and subsequently processed reminders) are recorded in table civicrm_action_log with an action_date_time value of NULL.

Ref:

CRM-20143: Advise admins about invalid "action.*" tokens