I have a similar crashing issue that appears to be related to the number of Chickens/Cows/villagers are loaded in memory...

• when I kill off animals, the issue improves
• when I bring more animals back, the issue returns
• when I go far enough away from my base that the animals are removed from memory the game stabilizes. 
• Happens across multiple worlds and across multiple iOS devices (tried ipad mini and iphone 6... no perceived difference between the 2 devices... the crash happens before the game slows down.)