At least three times over the past few weeks, iTunes Match has spontaneously reset itself on my Mac. By this, I mean that the iTunes Match item reappeared in the Store section listing. Selecting the item revealed that iTunes was again proceeding through the three steps of matching all of my music (Step 1: Gathering information about your iTunes library).

I have no idea what precipitates these resets. It doesn't appear to be due to anything I have done. I suspect some hiccup occurred on Apple's servers.

While the rematching remains mysterious and irritating (as it can take hours for the process to complete), it gets worse. Most often, the rematching never completes. Either it simply hangs, with no message and a progress bar that never moves, or an "unknown error" message pops up, suggesting that you try again later.

When this happened to me, after retrying three or four times, I have success: the matching completes and I am back in business. However, others have not been as fortunate. A search of Apple's Support Communities reveals () numerous users with the same symptom that remain stuck no matter how many times they "retry."