I'm seeing a few albums that i collected during the same time period show up as unavailable. It's actually a lot of albums. I already learned to live with radio-only licensing restrictions, but at least then i could find the content i liked on a different service if i really wanted to go back to it. See the ones only titled "This content is no longer available on Pandora" - surely hiding the artist and album names isn't intentional??
Although the majority of the songs in our collection will be eligible to be played without restrictions, you may encounter a portion of songs that are unavailable due to our current licensing restrictions.
We are continuously working on increasing the amount of songs which can be played on stations, on-demand, or offline. Our intention is to provide enough music you enjoy to avoid any inconvenience around this.
This being said, that does look like a bug where those tiles still showed in your collection with that error showing.
I went ahead and removed those for you on my end so they no longer show in your collection.
This being said, there isn't a way for us to verify what those collected albums were that were no longer available.
Hope this helps, and we apologize for any inconvenience.