Hi,
I created a bug report for this issue that can be tracked here if/when it’s approved for public visibility: https://issues.unrealengine.com/issue/UE-320638. There is no ETA as priorities for bugs and features can shift at any time.
In the meantime there are two workarounds:
1.) Blender adjusting the rotation affected to 90 and setting the scale to be .01 - according to this discussion https://forums.unrealengine.com/t/unreals-socket-import-for-fbx-files-is-broken-workaround/2303521
2.) In Unreal, in the static mesh editor go to Socket Manager, click on the socket and reset relative orientation and scale
Regards