Workout playlist only plays one app on watch and I have to manually select the next one

Originally, I was able to set up a playlist workout, which worked fine on my watch as soon as the workout started, and only stopped when I finished the workout. Now, I have to connect my Sony headphones every time, and I can only play one track from the playlist and I then have to manually start the next one. I can't see what I may have done to change this.