Erratic Behaviour from .NET MemoryCache Expiration Demystified

On a recent project I experienced first-hand, how the .NET MemoryCache class, when used with either absolute or sliding expiration, can produce some unpredictable and undocumented results. Sometimes cache items expire exactly when expected… yay. But mostly, they expire an arbitrary period of time late. For example, a cache item with an absolute expiry of 5…