Hi there!

Well depending on your situation there isn't too much to go on for that one, either it can be a graphical glitch, or a re-positioning issue if your client side doesn't update the area fast enough, but there's a much simpler explanation given the dungeons you just gave me. In Haukke Manor's last boss, there are some objects that will continuously inflict health damage unless interacted with it, this can cause the appearance of health loss without needing to be attacked, and for Brayflox's last boss there are a few moves that can cause damage without having to be in range of an attack, for instance the "ground pound" which causes raid-wide AOE if you're in too close proximity to the boss that drops rocks while occasionally knocking you back and there's also the AOE poison that will make you lose health if you step inside it. These are just some speculations since there's not much here to go on. More details would be nice, but here are just my two cents