I'm encountering the offhand disarm bug others have mentioned, but that I don't think anyone got to the bottom of. I have offhand at 99%, and I have the ambidextrous disarmer edge. Offhand disarm fails nearly every time I use it whether on a PC or on a mob.
I also have the ability sometimes take two rounds and sometimes one. I'm not 100% sure, but I think in the past it's always been 1 round with the edge. For sure, its success has been more consistent.