What you were expecting to happen, and what actually happened?
Usually the Monster Difficulty did not apply to PvP but to my surprise my couple of PvP games have 200% (Warlord IV) applied to it 
What are the steps to make it happen again?
Play PVP on Warlord IV difficulty
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!
None but reproducible
Hmm… Odd not reproducible anymore. I noticed at that time in PvP menu that I can adjust monster difficulty consistently. now after restarting the game, the option is no longer there. Really puzzling. Was pretty sure not in explore mode as i can choose 3 opponents when that happens
Maybe you were in casual pvp? Cause you can adjust the difficulty there
Hmm… So it seems. My bad. I did not noticed I selected casual PvP