I had a similar problem with HST Mk3s earlier today in fact - half an 8 coach rake left the track after derailing on a track join where I'd not put it back together properly (temporary track arrangement, not tacked down). At higher speeds little imperfections have more dramatic consequences... There was a pronounced 'click' as each coach passed over the join, and after a couple of loops at high speed, a coach in the middle of the train bounced, and that resulted in all the trailing coaches derailing too.
Another derailment problem with the same rake was caused by the hook-couplers between the end coach and power car getting tangled when going round bends. Happened to any coach in that last-but-one position in the train. The only solution was to take a hook off the coach and leave the one on the power car. Probably not much help with the Pendolino as it's a different coupling mechanism isn't it?
Just a thought if the problem reoccurs, see if it happens if you run the train in reverse. To be fair to the rear power car you'd have to turn the whole train around.
Another derailment problem with the same rake was caused by the hook-couplers between the end coach and power car getting tangled when going round bends. Happened to any coach in that last-but-one position in the train. The only solution was to take a hook off the coach and leave the one on the power car. Probably not much help with the Pendolino as it's a different coupling mechanism isn't it?
Just a thought if the problem reoccurs, see if it happens if you run the train in reverse. To be fair to the rear power car you'd have to turn the whole train around.
