Why are purchased iTunes albums missing tracks, requiring repurchase?

I purchased complete albums through itunes and have had them in my library for years. Now albums are showing as incomplete with missing tracks, for example, on March 16, 2016 I purchased the entire album "Some Girls" by the Rolling Stones for $9.99. The album has 10 tracks. Now the album shows only tracks 1, 3, 7, 8, 9, and 10 as being available to download, and I need to repurchase the album to listen to the missing tracks. I'm using the same apple ID. I removed the download, hid the purchase, then "unhide"d the purchase twice, but no difference. What gives Apple?