Tried to play around with it some but just don't have the time to really go into it. However, if you check the default animations file, you'll find the correct loc for Gauge fill. Your current locs are off. By adjusting the locs, I was able to get solid bars. That's as far as I got, but then fubared the file and deleted it shortly after
In a normal color change window, as the health bar depletes, the colors change. You start with, say green, then at 75 you change to yellow, then at 50 orange, then at 25 red.
However, you are attempting to basically make it change where the whole thing is grey, then red at 99%, then yellow at 75%, then gray again at 50%. Feels like maybe you're missing a layer.
Also, once you get it working on player health, you're basically going ot have to completely flip all the sizes and offsets in order to make it work in reverse for the aggro meter ... this seems like an ambitious task and I hope you crack this!