I’m also a Biped user. just yesterday I finally managed to use Anim Retargetting from UE4’s blueman into my Biped-based skeleton
for me it’s really important to keep using Biped because I have over 115 animations that I made for my UDK game, most of which I’ll want to re-use, but need to copy-paste into my UE4 skeleton which is slightly different from my UDK one - and for copy-pasting into a different skeleton Biped is the best.
but I also want to use some of the marketplace’s animations, which is why it was a priority for me to get the retargetting to work
now I didn’t know such a setup would cause problems in PHAT, in UDK I actually didn’t use twist bones (I vaguely remember problems similar to what you describe, from when I did try)
I guess this means my proof-of-concept phase for animation isn’t over yet, until I try and test PHAT as well and make it work 