Animation error with rig

Hi guys, just got back into unreal after a year or so away. was a newbie before but wandered if someone could help please. why do bones sometimes go dolally when imported into the engine?

Case in point, trying to import the running animation for my Inspector Gadget character and his jaw’s kinda inverted itself,
another one, fingers randomly reposition themselves from the exported animation… any ideas welcome

looks kinda like he’s sucked a super lemon