I have the same problem - they AREN'T hidden. They aren't visible on computer, iPad or iPhone with match on. Obviously something screwed in the purchase history. Even if I have backups they will count against the 25,000 track limit for iTunes in the cloud - which is a bit of an issue as I have 24,997 non-purchased track already.
A bit of an issue for someone who's bought a lot from iTunes over the years - and not helped by being unable to get an answer from support. Oddly if I switch match off a few of them become available.
Any suggestions - apart from contact support (I'm still waiting) - appreciated