I think I can see the issue. If you had a song loaded in the player, then clear the queue so that the player is hidden, it will stay hidden when you select the next song. I will take a look at this.
In the meantime just make sure your queue does not run empty. If it does, select a new song and when the player does not appear, just restart the app. The player will then show again.
I will try to get this fixed today and have an update ready by tomorrow.