Broadband drops to 12Mbps every evening since last week

Anyone else getting horrible evening slowdown with Nexora broadband? Ours is fine through the day, then around 7pm it drops like a stone. Speed test just now was 12 down on a package that should be about 150. This has been going on for nearly a week and it’s driving me mad because streaming keeps buffering. Router rebooted, cables checked, all that. Is this just the normal 'peak time' thing or is there something wrong?