Apparently, there is an audio library issue that freezes Samsung phones when the screen locks. They are working on it.
From Jon (Ludei Support):
Ok, good news! After updating the audio library to the latest version (which has quite a few fixes), the hang no longer happens in your game
We'll go through our usual round of testing, and hopefully this fix will make it to production during the next 2-3 weeks.
Thanks again for reporting!