I'd agree that the evening trains leaving London Bridge seem to work to a somewhat random schedule. I usually catch the 17:30, 17:40 or 17:50 and these seem to be consistently delayed usually due to late arrival of the inbound train. Last night they excelled themselves by delaying the train for about seven minutes as the driver was on their break. I would have thought they could have scheduled the train departure and driver break a bit more sensibly.