This has started to happen recently with my TP-Link Archer C80 router. It shuts down (powers off) when logging onto the fiber provider's network. I've had to default to my old 100Mbit router also from TP-Link in the meantime which works OK. If I disconnect the router from the ONT it lights up and stays lit obviously not able to login to the ISP. But once I connect to the ONT the router shuts down. It's not a faulty 12v power cable as I tried with 3 different ones and different 12v power supplies. Has anyone had something this weird happen to them?