I've been surfing on YouTube lately and I came across a recent video of a 1972 tube stock car failing to open its doors on a Bakerloo line journey, the OP identifying car 3559 as the culprit, running at the rear of a southbound train. The video opens with the train having not opened its doors at Kilburn Park, then upon arrival at Maida Vale it failed to open its doors again. I presume that other doors throughout the train opened as usual, as it can be heard in the video. The driver noticed something was wrong when attempting to start, before the issue was somehow resolved by the time it reached the next station, Warwick Avenue, when the doors reopened like nothing happened.
I'm left puzzled over what fault could've been, perhaps the driver had mistakenly left the rear sets of the doors locked?
I recall, in the early days of this stock, a casual flick of the twin open buttons by the train guard resulted in some cars having no doors opening. Must have been end-door cut-out buttons back then for the short Northern line platforms such as Charing Cross, with the front double doorway cut out on the northbound, and the rear double doorway cut out on the southbound. At the northbound platforms of Hampstead and Camden Town, Barnet branch, the rear double doorway is cut out, whilst on the southbound line the rear double doorway is cut out at Euston, Bank branch, and Clapham Common, but the front double doorway is cut out at Moorgate. [Response to FoI request FOI-1608-2122 published 24 November 2021] Perhaps OPO conversion for the Jubilee and Bakerloo lines avoided this complication as all other tube lines have no need of it.