Movie’s disappearing from collection

So I may have stumbled on something shortly after posting the above AND might be able to explain why @anon18523487 didn’t see an issue…

Some but not all of my libraries have been in place for years and after posting, clicking around, and reading some other problems here in the forums, I discovered the “Upgrade Library” feature that’s not getting the best of reviews. I bit the bullet and upgraded one of my old libraries, recreated a collection that I deleted because it wasn’t working, added movies, and they’re still there after clicking around and refreshing a few times…

Then I rebooted and the collection is still there with the movies I added. Could this issue be stemming from old libraries that were created prior to whatever magic happens under the covers with the “new” libraries? In other words, are collections not compatible with old libraries???