A persistent, flashing amber light indicates that any of the several potential conditions may require your attention:
• The base station has not yet been configured because it is new, or the reset switch has been set.
• You have selected a security configuration that is not recommended.
• A new firmware update is available for the base station.
• One of several other conditions, such as a disconnected Ethernet cable or invalid IP address has been detected.
ref: [https://support.apple.com/en-us/HT202211|AirPort base stations: About AirPort base station status lights (LED)]
To find out why your base station's status LED is flashing amber:
• Open AirPort Utility
• Click on the AirPort base station
• Look for a Status setting in the small window that appears. Note: Status only appears if there is an issue or notification.
Click on the small amber dot there and another window will open to explain what the "issue" might be.