The first generation copies of some of the transmissions from Apollo 11 have been misplaced. They do still have essentially copies of copies of those transmissions, however.
There are apparently 700 missing boxes of magnetic tapes, most notably including the high-quality recordings of the video feed from the Apollo 11 moonwalk. Wikipedia has a summary and there’s a more detailed account here (a pdf).
Whether they are missing or not, magnetic tapes from that era are fast deteriorating to the point of unreadability.
A lot will depend on their storage conditions, how often they they are rewound, etc. But even under the best conditions, mag tape starts to deteriorate at about 10 years old, according to some experts, and nearly all the experts agree that 30-40 years is the outside limit. The NASA moon landing was 40 years ago.