There’s been dozens of test runs as well before the first westbound trains that used it in anger yesterday and this morning. That it’s happened to just one cover, not all of them (they’ve had a visual inspection as part of the recovery of today’s incident) would, in my mind, rule out vibration issues as a cause - although it may still be an aggravating factor. We could speculate until cows come home. End of the day I have no idea why it happened, just that it happened and reported as such on here the facts I know.