What you were expecting to happen, and what actually happened?
Infernus’ ability says: Deal [Magic + 10] damage to 2 random enemies, and half of that damage to adjacent enemies. Explode 5 random Gems.
The second random shot used to resolve after the first one, meaning it had a separate animation and it couldn’t target enemies killed by the first one.
Now it still has a separate animation but it can target enemies killed by the first shot. Sometimes the animation is either missing or barely noticeable if it targets a dead enemy.
What are the steps to make it happen again?
Use Infernus’ ability to kill enemies, no extra steps required.