I have a similar gripe re: Tidal. There are so many "re-recordings" of songs and they are not the same. Old doo wop songs are a prime example. As to why some titles disappear, I'd like to know the reason for that too. I complained to Tidal and wondered why some titles that I had added to my playlist disappeared after a short time. The answer I got was something about the rights expiring. Not sure I understand that, but it's frustrating to find some titles and versions of songs you like, then they're removed. I have noticed that sometimes there are different albums with the same songs on them and you can go to another album collection and re-download the song, but not always. It seems that's why you're paying them: to provide a service.
(BTW, if you're a veteran Tidal does offer a nice discount)
(BTW, if you're a veteran Tidal does offer a nice discount)