Seems like some kind of media player, but doesn't look like the stock Samsung music player. In any case, can you press & hold it, then drag it to a trash can or Remove icon?
This happens to me when Spotify for some reason goes berserk and leaves the lockscreen controls there even after I stopped playing any tracks. But yeah, it definitively is a Media Player app that's triggering that. You might wanna check your media apps and see if any of them are going rogue.