Internet connection fails when Airtime Fairness is on

Symptoms

F-Secure SENSE Router is connected to an upstream router via WiFi. In the upstream router settings, the Airtime Fairness option has been enabled. The SENSE Router screen shows the disconnected symbol which means that the internet connection to SENSE Router is down.

Diagnosis

We have tested this with the Sagemcom FAST3686 cable modem, and it seems that SENSE Router does not support the Airtime Fairness option enabled if SENSE Router is connected to an upstream router via WiFi.

Note: If, however, SENSE Router is connected to the router via Ethernet cable, the internet connection works without issues.

Solution

To restore the internet connection:

Disable the Airtime Fairness setting in the upstream router settings OR
Connect SENSE Router to the upstream router via cable.