I'm on an iPhone 6 Plus running the latest version of iOS. When using the default music app from Apple, song titles and whatnot display just fine. Whenever I use Spotify, though, no metadata is transferred. I just get place holder titles like "no title". If I connect my phone via USB instead of steaming over Bluetooth, the data shows just fine, even when using Spotify. Interestingly enough, if I let Apple Music play a song over Bluetooth and have its metadata stream over and THEN go back to Spotify, the song data all shows up. I've tested this on my girlfriend's 5s, as well, so I can verify that this is not an issue with my phone specifically.

I'm attaching some photos showing what I'm talking about along with my car's software info