I've been using the Spotify app from Mini Connected on a 2019 Mini JCW. Everything works fine, except that when I try to skip tracks using the steering wheel buttons a message displaying "Loading" shows and nothing happens. I'm able to skip tracks using the radio seek buttons or the screen buttons but nothing from the steering wheel.
No fix or solution, but just wanted to say I have the same issue - or actually worse as skip doesn't work at all for me. If I connect with cable most often spotify won't even show as an option. Using Bluetooth I can always play, but skip buttons doesn't work. Neither on wheel not on the headunit. As a test I installed Apple music for Android, and in this app the skip function works like a charm (Only tried with bluetooth) so issue is for sure with Spotify and not android.