I have just been defeated by an elite blue pack from act 3. The issue is that all 3 monster are in flame, because they had to cross a firewall to reach me, and now, they are "burning", which doesn't affect their life, but when i "touch" any of them, it's like I am into the firewall. I discovered this when I died from the firewall when I was in another room with the elite pack. There is a screen shot here to give you more informations.
I was coming from the south east, going north east when they apeared normally, they limit of the upper right map is where is located the firewall they had to cross through. We can also see that they are "burning", and the "Mur de feu" is firewall in french.
I was playing alone in a private game, in PM5. I never crossed the line where the firewall can appear sometimes. It was not a lag I really think it is a bug.
Please, let me know about this.