WWAN packet loss after WAN disconnect

Hi all,

when I disconnect the WAN port, WWAN connection experiences increased ping time and packet loss.

I have a USB Wifi adaper connected (in Client mode) to an AP which provides a secondary internet connection, while WAN is connected to my primary ISPs router. When both are connected, mwan3 shows both connections are up and running and WWAN shows a stable connection with stable pings.

As soon as I disconnect the WAN port (Gbit cable), mwan3 switches to WWAN, but while the wireless connection seems to be up and running, the ping times increase by 100x and I see a 95% packet loss.

It seems to me like the wireless connection somehow relies on the wired WAN, because when I reconnect the WAN connection, WWAN stabilizes and pings as well as packet loss normalizes.

The only connection between these two interfaces is the shared Firewall zone, both are in the wan zone.

All suggestions are appreciated. I'd like to get to the bottom of this myself but need some advice what to look for. Many thanks in advance