Connection status on the admin page should read CONNECTED. If it says REAUTH REQUIRED, click Reconnect Square.
Location enabled: the register's location must be ticked under Square connection.
Order source: by default POS and Square Online orders show. Enable Show orders from every source to include others.
Old orders: orders older than the "Ignore older than" setting (30 minutes by default) are recorded but not shown, which protects the kitchen from offline-POS catch-up floods.
Board connection: the header shows live, reconnecting, or polling. Polling still works, only slower.