I have noticed, at least on my Beastlord, Playing possum as well as Falsify Death acting as if I have fallen to the ground but nothing stating that I have moved or fallen to the ground. Falsify Death shouldn't even fail as it is instant de-agro. I am not certain as to the cause but I believe that it is tied to Dot's. It is my belief that if I am to FD right about the time that my dot's tick on the mob, it does not dump agro so I am just lying there while being attacked.
Do not meet a see-through mob at the fade destination. Also, level. I think it will be somewhat better from level 95 Playing Possum rank 8. Falsified Death https://www.raidloot.com/aa?name=Falsified Death Playing Possum https://www.raidloot.com/aa?name=Playing Possum
I don't know what you're trying to say. Lying on the ground FD however doesn't matter if the mob can see invis or not.