I know it’s been over two years, but maybe this might help someone else.
I had this same issue, in my case it was caused by using the wrong default scale in Blender. Following the last section in this guide resolved it for me: Driving Around: Exploring Chaos Vehicles | Talks and demos
"Blender and Unreal have an incompatibility regarding the default scale when importing an .fbx model, so in order to import it properly, we need a workaround before exporting a vehicle Skeletal Mesh from Blender. Do as follows:
- Select your Armature object, press S for proportional scaling and set it to 100.
- Press Ctrl+A and apply the scale transforms to the object.
- Head to Scene Properties > Units and then set Unit Scale to 0.01.
- Export your mesh as .fbx."