Massive track circuit problems around Borough Market, between Waterloo East and London Bridge. Heard one was showing occupied when it was actually clear. Began around 17:50 and fixed around 22:00 if I remember right.
For Southeastern, services between Charing Cross and London Bridge were going through slowly one by one or went via Cannon Street and the single line Metropolitan reversible. This in itself meant severe delays because of the wait to go through the section or the diversion via Cannon Street. Obviously this also impacted on services leaving Cannon Street, as the platforms and throat were congested with extra services not timetabled to be there.
For Thameslink, trains between Bedford and Brighton via London Bridge simply avoided the area and were diverted via Elephant and Castle instead, adding some delays to their journeys too.
As with everything at London Bridge, once one thing goes wrong, it all falls and the congestion caused multiplies over time. If a major issue happens in the evening peak, service will more than likely not recover for the rest of the night, as is the extent of stock/crew displacement.