This has always been a pain about streaming services. The reason is almost always some licensing dispute or contract running out between the publisher, streaming company, and artist. Same kind of thing as when Netflix loses a movie or TV show. This is a good reason to still buy LPs, CDs, or DRM free mp3s since, for smaller artists, getting those rights back may not be worth bothering with for a giant like Spotify or Apple.

I'm not aware of this happening for explicitly censorious reasons, but I wouldn't be surprised at all if it did.