Thanks for the replies. I've tried both settings regarding the lock screen and had no luck. It's not a major issue for me as I can control it from my watch but it's something to be aware of moving forward. Keep up the good work. Poweramp is still the best music player on the market.
On my Xperia Z5 with Android N the audio controls no longer display on the lock screen whilst music is playing. The album art displays perfectly and it works fine from the home screen. This all worked fine under Marshmallow.