Bone stretching on exported animation (UE standard animations play fine)

I have a custom character with special proportions fit to a mannequin 5 skeleton. When I bring him into unreal, everything plays fine, I can run all the animations on the other characters. However when I export an animation from Maya, the bones seem stretched.

In maya, I don’t think I’m doing anything special. I’ve baked the animations from the root down. I’ve even gone through to check that there is not translation animation on any bone except the hip. Yet when I bring it into unreal, things are stretched in weird proportions. It feels like there’s some translate animation coming through, but I don’t see it on the bones. Could anyone shed some light on what might be
going on here?