Networks hand out permissions for a limited time (LinkedIn 60 days, Pinterest 30 days, Facebook user sessions 60 days) or revoke them when you change your password or remove the app. When that happens:

• The channel shows Expired on Social Channels and on the dashboard.
• Scheduled posts for it are paused — nothing is lost.
• Channel managers get a notification and, by default, an email.

Fix: Social Channels → the ↻ button on the channel → sign in again. Paused posts resume automatically.