iTunes Match and missing artwork

I'm new to the iTunes Match, subscribed after my Music expired.

Now, I can't get my album artwork to sync. Everything works fine on my Mac. It syncs and so on. But when it comes to my iPhone, or iPad, or my Win-PC, no artwork is shown. Only a few weird ones. And, I'm speaking about the artwork iTunes found for me from the Store. If I've manually added any artwork, it syncs just like it should.

I've tried everything except adding every single album cover manually. That's the last thing I'll try. But before that, any suggestions?

Everything is up-to-date.