Anomalous Entity Disappearance

Anomalous Entity Disappearance describes a phenomenon in which random entities (Such as NPCs and enemies) are permanently removed without a trace, and any entities that have been removed by this anomaly cannot be brought back through any means. This will usually happen with no warning and can happen at any moment. This can result in the game becoming impossible or unplayable due to a variety of reasons, such as one of the bosses being removed entirely. Usually, this is a sign of a failure within the Personalisation A.I. which in and of itself can render a cartridge unusable.

Behavior
This anomaly is incredibly rare, and has only been reported in a select few copies. Prevention for this anomaly is unknown, meaning that it could possibly happen to any copy with usually no sign it is about to happen. Corruption and other similar errors have only been reported once in a copy with this anomaly, and they seemingly had no connection.

An absolute cause of this anomaly, other than the given information that it's a sign of failure within the Personalization A.I. is currently unknown. However, some theories and reports of this anomaly suggest that repeated cartridge tilting may have something to do with it. Currently, these theories have yet to be confirmed.

Theories
As said above, some theories suggest that cartridge tilting may have something to do with it as more than one report of this anomaly particularly note that there was a lot of cartridge tilting at all. These theories have yet to be confirmed as a good portion of other reports don't have cartridge tilting noted at all, so whether or not cartridge tilting has anything to do with it is up for debate.

Another theory is that corruption could be a possible cause for this anomaly. The only evidence for this claim is the simple fact that corruption can cause the game to try to not use too much memory, causing a bunch of bugs and errors (Such as not allowing you to enter paintings, and enemies' shadows turning into white boxes) However, this theory can be disproven by the simple fact corruption does not work on original hardware.