Previously I was having issues with the sharing function as well as trying to get Spotify to play songs sent to me through Facebook Messenger. After a recent update though, those problems were semi-gone. The sharing function was back and now I was able to open song links my friends sent to me.
At first, it was working fine then when someone sent me a link to a song on messenger and I tried to open it, Spotify didn't play the song. So I thought the function was messed up again but then I realized later on that it was only choosing to open and play certain songs.
Initially I thought it was only my friends who had iOS devices whos song links were working but then my sister who has the same device as me (Galaxy S9+) sent me a song and I learned it wasn't a iOS/Android problem. After experimenting with a few more different tracks and ways to share I realized for some tracks when you share using the 3 dots on the top right of the main song page then the link will not work, but if you share using the share icon on the bottom right of the main song page then the link will most likely work.
I say "most likely", because there was still a few tracks that did not play at all no matter which route I took for sharing. This is very strange and of course very inconvenient and frustrating to me as I am in a band and I share songs and receive song links through Messenger daily so I'm wondering if anyone else is having this issue.