“The network cable is unplugged” on RT-AX88U@ .11

I’ve just upgraded the firmware to the latest .11 version released yesterday and now router just says, that the network cable is unplugged for the external connection. The corresponding led on the router is turned off, there is no red indications or something like that.

I’ve tried to fallback to .10_2 I’ve had previously, the UI looks like updating, then it asks to reboot manually and after rebooting it’s still stuck at .11.

I’ve tried resetting the jffs partition and flash the .11 again – still the cable is unplugged.

Just right now, after waiting for 10 minutes – The status light suddenly goes red, the notice on the network map changed to “Disconnected” and soon after that everything starts working again.
I’ve checked again, cycled the power – and here we are again, the led is off, “the cable is unplugged” in the status is displayed again.

What can I do in order to check what’s wrong with the router? The fact I’m unable to rollback to 10_2 really bothers me.