The AWS fault which caused the 810 to stop may be significant. RTT shows no other train on the fast line nearer than St Albans at the time of the accident, so the 810's driver should have been seeing green signals and getting an AWS bell. If either of those didn't happen (and in particular if only one of them did) the driver would have noticed something amiss and stopped. (there are three possibilities, a fault with the signal itself, a fault with the trackside part of the AWS equipement, or a fault with the trainborne AWS equipment)
Again, if the 810 was under green signals it might have taken more than one block to stop - that is after all why double yellows exist.
So an important question will be what the driver of the 360 saw and heard when passing the same signal.