I don’t know if your problem was related(Windows Update has so very many quirks up its sleeve); but the timing makes Microsoft’s recent release mixup seem like a possible suspect.
If there was a prior warning, it could also have just been one of the ‘feature’ updates(like 1607 or 1703); those take ages to install if you don’t have a nice fast disk; and nontrivial amounts of time if you do. Particularly if your stock business-class antivirus is grovelling over everything they do during the entire operation.
