Scheduled Reminders not being send
Check under Administer>System Settings>Scheduled Jobs and make sure the job is enabled. It should also show when it was last run.

If it is enabled you should make sure you have your cron job setup correctly. More info on that is here: https://docs.civicrm.org/user/en/latest/initial-set-up/scheduled-jobs/#initiation 

Hope this helps!