So, I'm guessing that most people have noticed that combat seems really swingy: you often either take massive damage or just completely steamroll the enemy. Well, I think I figured out why.
When you reload an area, the Damage Threshold of the enemies in it drops to 0.
Steps to reproduce:
1) Start a new game
2) Head to Dyrford Crossing
4) Attack the first group of beetles you see. Look at the damage you're doing to them and hover over a damage line to get the attack breakdown. You should see something like "33.6 - 30.0 = 3.4 Slash Damage".
6) Attack the same group of beetles and look at your damage again. This time you should be getting something along the lines of "33.6 - 0.0 = 33.6 Slash Damage"
The beetles should still have their 30 DT after you load your save!
As you can see, this can change the difficulty of an encounter massively, especially against heavily armored enemies like the beetles.
The bug seems to occur when the game reloads an area you have previously visited. In other words, the first time you enter an area with a character, enemy DT works correctly, but if you either save and reload afterwards or leave and re-enter the area, enemy DT drops to zero.