Usg Flex 200 - Failover with trunk

Hello,

I set up a failover using trunk as explained in the tutorials.

It works fine when I test by physically unplugging the wan1 ethernet port (2)

But if I only disconnect the cable side of the cable modem, the failover on wan2 stops after a few seconds, and the only difference I see in the log is an entry msg="a connection timeout occured" cat="Myzyxel Dot Com" .

Any idea ?