Managed to get this resolved after a couple of further attempts with guest relations. The date stamped photo from the room was a very helpful idea... I might start to do that as a new habit! I'm not sure, though, that this was the result of accidental logging as a no-show, as I'd have thought that would have invalidated my digital key, which remained working?

Good to know, also, about the internal systems in case it happens again so I can request it there and then.