As Nathan mentioned, check if you're using the traffic, cron, or cloud:
traffic - you will need to have visitors on your community's front-end for these tasks to process. if traffic is minimal and you're self-hosted, running tasks manually or cron will be a good idea.
cron - likely your cron is failing and you'll need to have your server administrator check the logs. Can post the error here.
cloud - if you're on our Cloud, try navigating the front-end to kick start the tasks. If they don't start moving, please submit a ticket.