1. What happened
These 2 fbx characters import with the correct arm pose (T-Stance) in 5.0
These 2 same characters import with a bad arm pose (pointing strait forward) in 5.2
See attached comparison images and project containing the two fbx character files... Adam.fbx & Zoe.fbx

note: In 5.2, there is an import warining about inbetween joints, but it should still import properly, like it did in 5.0

2. How we can reproduce it using the example you attached
Open Project
Open BadPose scene

or...
Copy the 2 fbx files into a new project
Drop Adam and Zoe into a new scene