According to tubestatus.net/timeline/date/2018-02-09 the issue was northbound, resulting in a part suspension from circa 05:30 to circa 06:15 (the site just takes snapshots every 15 minutes so it's not possible to be more finegrained than that)
No service between Victoria and Highbury & Islington northbound only, while we fix a fault with the track at Kings Cross. Tickets will be accepted on Greater Anglia, Great Northern, London Overground and London Buses via any reasonable route. Tickets will also be accepted on South Western Railway between Vauxhall and Waterloo and on Southeastern between Brixton and Victoria. GOOD SERVICE on the rest of the line.
There was allegedly a good service on the rest of the line, which seems impossible as the south end of the line would get full much sooner than 45 minutes after a suspension.
The essential things in life are seen not with the eyes, but with the heart. --Antoine de St. Exupery
A combination of signalling problems at Walthamstow Central from the start of traffic and a broken rail at King's Cross requiring a re-rail. Essentially the Vic was running in two sections, Brixton-Victoria and Highbury-Walthamstow.
Looks like the signal system issues came back with vengeance this morning resulting in a one hour suspension of the service between approx 08:45 and 09:45. As of now (12:50) services are operating with minor delays whilst gaps in the service are plugged.