Purchased music disappearing or greyed out in iPhone Music library

I have purchased a lot of music over the years, and slowly it seems to be disappearing from my music library on my iphone. Some of them I can see but I can't play (they are greyed out). Some don't show at all. At the suggestion of another site, I checked in my setting for hidden items and found them, but when I clicked "unhide" they disappeared from my hidden items list and still do not show in my music library. What else can I do?