You're not alone. I'm in the same boat.These so-called improvements and "upgrades" only foul up my music collection. I'm beginning to wonder if the only answer is Google Music.
I too have been hit with this. I have one Mac, and only one Apple ID for iTunes. I too had the issue where iTunes Match would somehow turn itself off every few days. I've contacted support via Express Lane.
What's really comical is that based on the warning I just got, this device had been associated some other Apple ID 53 days ago, when I know for a fact that I've used iTunes Match within that timespan on this very same machine, with the same Apple ID.