iTunes Match is stuck at step 3 while downloading album covers and the remaining pieces. In this case is almost as common as the blocking step 1 and hence rule out the same way.
Beyond synchronization, several more or less serious problems may affect iTunes Match. Why some songs are not synchronized. Several reasons may explain the non-synchronization of certain pieces. The easiest way to check is the number of songs you have: iTunes Match cannot store that 25,000, not counting those that you purchased from the iTunes Store. The number of songs in your library appears in the status bar (View> Show Status Bar) for Songs or Artists.
Some songs are not eligible (they are followed by a cloud icon strikethrough): those who weigh more than 200 MB or are encoded with a rate of less than 96 kbps (see summary information panel). To our knowledge, no store has proposed lower quality music at 128 kbps: the latter must have been intended to limit money pirated music. We have managed to achieve against the first limit with long pieces of classical or jazz ALAC unless you want to convert a destructive codec, there is currently no solution.
An icon representing two clouds crossed on a song supposed to be replicated. iTunes Match sometimes confused in an album version and a version in a compilation or two interpretations of the same song in an album "deluxe" or an anthology. You can try to force the addition (Add to iCloud in the menu), but most of the time, iTunes Match will remain bounded. Remove the piece of iCloud and importing again is an effective solution, but difficult and which is also not always feasible.
A cloud containing an exclamation point indicates an error: Update iTunes Match (Store> iTunes Match) is generally effective. If you can, enable and disable iTunes Match (if necessary by holding down ⌥) or force the addition. If nothing works, it is possible that the piece is corrupt: there is not much to do other than delete and import a new copy.
Some times Playback does not start on right time. If a song is playing in the cloud does not start, check the service status page Apple: if you cannot access it, is that you are not connected, so you can access, check iTunes Match is not just down. If the reading is still churning in a vacuum, it is usually because your session has expired: reconnect to your account in the iTunes Store. Restart iTunes is also a good solution.
In case of getting trouble in Playback stops being music / playback skips: Reading generally stops during the song when iTunes Match or skips a flow problems. Of course you can download the songs you want to play and delete once heard, but we have seen more practical. Unfortunately these hiccups can last for days and involve only certain songs and not others.