Trolleys get turfed off at Bristol if it's a bit busy, and with 2 car thats very likely.
18.22 off Bristol was also 2 car and v busy, with 3 cars sat just off platform 1 in the siding.
Assume the 3 car was poorly.
Belive 3 car was taken off of the 14.54 Cardiff, as that was formed 2 coaches down to Bristol from Cardiff, and the attatchment is booked 2.