This is happening to me as well. I swear if this is a "feature" change I'm leaving Spotify. I've found so many artists with this I was able to overlook that it wouldn't really give me a mix and just "low-key" shuffle around what was already there or had been there very recently.
Basically if I only one song from a particular album was in my daily mix enough times, it would ONLY have that one in the mix. I've had to go back and listen to a bands full album just to get it to start including other tracks from that release.
1) Storage for catalog of music
2) Database of catalog metadata
3) Index on data for common fields that are searched against
1) User login for authenticating their account
2) Local storage point for saving/caching
3) Input field for querying and searching local/remote data
Lol it's really not hard, on so many levels. This is not hard whatsoever but yet it somehow is.