Since the last update I encountered several times exploding Gems whilst playing. 
Can someone try to explain to me the how what why? 
I tried to find out what I want to know via the official pages but either the devs forgot to put it in there or I missed it. 
What was your team when you noticed the exploding? What was the opponent’s team?
Sorry folks, I found out where it came from. Was a new trait on one of my troops I missed 
So regards this topic as closed 