Why does it seem my skeleton is working fine in Blender but it completely fails in UE4?

I am very new to blender but after spending a few days I feel like I’ve finally given the mesh good weight painting. I can move around the joints and while there are a few flaws in it, it shouldn’t nearly as bad as it is in UE4. Note that the left is a photo from a pose, not an animation, I’m not sure if that makes a difference.

[Here][2] is the file I’m using. In it is Buzz and also the model with the Mixamo animation I’m trying to use for Buzz. I couldn’t find how to use that exact animation on Buzz, but I would really like to, because I could then determine if this is an issue with the animation or an issue between the programs.

It’s one solid mesh, pretty sure I’m using default settings, except for turned off the leaf bones. The bones have the weight painting on very close to the bones, except for the chest because Buzz’s chest isn’t that flexible, but that shouldn’t be affecting the legs which work perfectly fine. I think it’s worth noting that I am also able to bend Buzz into poses in UE4, so it appears this issue only comes up when animating.

Any ideas?

This is an issue that happens when you export as FBX.

Try to reset you rig in pose mode in Blender and apply the transform, rotation and scale.

If you use Blender 2.6x or 2.7x can use export the FBX with ASCII or binary.
This setting is removed in Blender 2.8x

Tell me if you need more help