Platform, device version and operating system:
Screenshot or image:
What you were expecting to happen, and what actually happened:
Based on this:
the assumption was that new Great Maw spawned by Copycat should not be able to keep devouring.
How often does this happen? When did it begin happening?
Every time you Copycat a Great Maw.
Steps to make it happen again
Cast Great Maw, summon another Great Maw with Copycat.