I found that the ANT pin needs to connect a π-type matching network for antenna matching.
In the test above, I directly use a u.FL 2.4GHz antenna connecting to ANT pin.
That’s probably the reason causing the unit not working properly.
I will try to utilize the antenna on the Air602 Dev Board and see if that works.
Update: I can program the Air602 WiFi Module with LuaTool (firmware AirM2M_Luat_V0011_W600T_USER.FLS), but the module does not respond to any AT commands.