GL-MT2500 Claims No Internet Connection

I’ve been using my GL-MT2500 Brume 2 in Dual-WAN mode (tether and Ethernet) for several months now. Beginning today, the Brume is saying “The interface is connected, but the Internet can’t be accessed.” for the Ethernet connection. I am still using the same two ISPs and the same ONTs. If I switch the two inputs to the Brume, the router continues to claim the Ethernet connection has no Internet despite which ISP it is. If I only use the Ethernet input and leave the tether unplugged, I can still access the Internet despite the message. I can also confirm that the Internet connections at both ONTs are live.

I’m fairly confident that in Dual-WAN load balancing mode (which is my primary use case), the Brume is ignoring the Ethernet input, so I’d really like to fix this. I’ve been running Firmware 4.5.0 for some time and still am.

Is this a known issue?

After the 4.5.0 update, the LED flashes blue and has the message that “it is connected, but without internet access”.
But the access is working, when I turn on the computer and access a website, the LED turns white and stops blinking.