If the main control board queries the Wi-Fi status as not connected to the router or server, the "Wi-Fi status icon slow flashing" indicates a U1 or U2 fault.

If this persists for 30 minutes, the "Wi-Fi status icon" will go out.   

The refrigerator does not report U0, which indicates that the main control board is communicating normally with the Wi-Fi module.

If  the engineer has checked the lines and found no problems,

it might be that the connection is unstable because the refrigerator and the router are blocked by the walls or interfered with by other metal objects.

Please place the refrigerator and the router closer to each other.