LearnDash LMS Notifications Addon 1.6.4

* Fixed issue where when a quiz notification was set in some rare instances this prevented the student from being able to complete the quiz

* Added ability to chose if the notification should only send one time or recurring for the trigger “User hasn’t logged In for “X” days
* Fixed email sending issue with group leaders
* Fixed emails sending in bulk on updating

* Added notifications can now be updated after they have been saved
* Added duration unit can now be minutes, hours, and days
* Updated the triggers codebase to improve notifications sending system
* Updated the log screen to make it easier to track what is happening within the system
* Removed the every minute cron and replaced with a single scheduled event to check rather than running blind checks