Can't see anyone else mentioning an issue on status pages etc so assuming it's a me issue.
Went off right on about 7.30pm today – have restarted ONT and UDM Pro, disabled DHCP on Quic account page (hadn't set it up to use it yet anyway).
Quic site shows PPPoe connected and can use the diagnostics which seem to indicate ONT is online and can communicate.
ONT lights on: Power, GPON and LAN1.