Be sure Autopilot is turned on. Click the 3-dot menu at the top right of SND Planner to open the Autopilot settings and enable Autopilot for the selected account.
Check that there is content available in the feeds assigned to the Automated Slot or Block. If all eligible content has been published, Autopilot will stop publishing until a new item is available.
Check for other manually created posts. If you have posted or scheduled manual content, the frequency interval between posts will start over. Publishing manual content frequently within an Autopilot block may keep Autopilot from finding an available time to publish.