Actually This problem can be easily done by "Copy and deleting music from your computer", and "move them back into "iTunes' Auto insert into iTunes folder (under your music folder)", iTunes will upload them again and it will be fixed.
The problem is due to the album only exist in your computer but was not phisically copied in the iTunes iCloud (Reason unknown).
Also sometimes you may find you want to update an incorrect artwork for an album. You insert the new artwork into the album and it looks fine in your computer. But after iTunes match re-sync, the incorrect art-work appears again. You just can not get rid of the incorrect artwork.
This is iTune's bug. You may be patient to wait until Apple fixes it, or do the following procedures to get it done temporarily with minimum effort. (I say temporarily because you may iadd new albums after you fix your current database, and the problem may happen until iTunes bug is fixed by Apple)
1. Turn your iDevices iTunes match off, remove all music on the device. make sure there is no music in it.
2. Turn the iTunes match on the iDevice again.
3. Your iPad or iPhone or Apple TV will start to download the Album info from iTunes cloud. While it is downloading, keep your iDevice on the iTunes app and drag through the album list. (Please use WiFi to do this step)
4. About an hour it should be completely synced. if you see artworks are missing, then it means the artwork does not exist in the iTunes cloud. No matter how you update in your computer it just does not upload into iCloud.
5. Creat a smart play list for "songs do not have art work" - then you should have a list of songs without artwork.
6. Drag them (copy) to a clean folder names "backup". Then you should have a extra copy in the folder "backup".
7. Delete the songs both from your computer and iCloud. (The copy in iTunes) then you should see those albums without artwork start to disappear from your iPad/iPhone etc. When you see no missing artwork album on ipad this step is done.
8. Move the extra copy in the folder "backup"
9. iTunes will automatically insert them back to your library.
10 iTunes match will start to upload them again to iCloud.
11. It should be mostly fine. If there is anything missing again, repreat from step 1 (because this is a bug of iTunes match - it just happens)
re-Uploading takes time but at least it your computer works not yourself.
Hope it helps.