I believe that you can see what's happening if you look at the armature with the octahedron bone rappresentation.
In the attached image you can see that the bones SHOULD follow the red-lined path, since a child's head must be cohincident with its parent's tail.
Szkaradek123 might it be that you're not correctly aligning heads and tails?
Furthermore, i noticed that the bones on the right side of the armature (left side of the image) is "flipped" upwards (as if mirrored on the blender file x axis: could it be that there's a "global" and "local" axes reference problem when importing?
I am ignorant on the subject, but could it be that you need to use a global axis reference for -all- bones, rather than a local axis reference? I mean, right side bones UP -must- be equal to left side bones up, right?
Lol you've hooked me on this problem Szkaradek123, what can I do to help you solve it?

