It was a fault in the Aberdeen seated coach. The stock is running empty to Edinburgh and will split as usual, 1Y11 runs as booked, 1S25 starts there as a passenger service and 1A25 cancelled with the coaches running empty to Aberdeen.
Couldn’t the faulty coach have been shunted out? That happened on one of my trips in Inverness last year and meant a very late departure but most of the time was made up by Inverness