What does AP LED flashing blue means?

Zyxel_HsinBo

Quick Flashing (Bright Blue, 300 ms)
Indicates that the AP is operating in Repeater mode and is attempting to connect to a root AP (uplink).
If repeater mode is not expected, please check the Ethernet cable and the connected uplink port to ensure the wired network connection is functioning properly.

Slow Flashing (Dark Blue, 1 second)
Indicates that the AP is performing a Channel Availability Check (CAC) on a DFS channel.
During this process, the AP temporarily suspends wireless service to verify that the selected channel is free of radar signals, as required by regional regulatory standards.
This behavior is normal, and the duration of the CAC scan may vary depending on the selected channel and local regulations. Once the CAC scan is completed successfully, the AP will resume normal wireless operation automatically.