I found that quite a few animators in the market are wrong about the rotation of the pelvic bone part of UE4 mannequin . 
Their misinterpretation resulted in the pelvic bones of the UE4 mannequin in their animation generally being so severely tilted back. 
As a result, when their animation is applied to the actual character model, the pose may be very awkward… 
Because of the special nature of the pelvis, it is the root of all the limb bones except the root bone, and it may be difficult for the user to correct. 
Referring to APose, the pelvis is already upright, but they actually flattened the yellow line in their animation, resulting in a severe posterior tilt of the pelvis in their animation.
Imagine your torso bending like a

!
And in terms of the human body, the angle at which the pelvis can tilt forward when standing is much greater than the angle at which it tilts backward
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Thanks for sharing! 


An example of a mistake,Note that when a person stands with the upper body upright or even leaning lightly forward, the pelvis should not inexplicably tilt back.
(PS:This image is cut from the show image of an animation with such problems in the UE market)
↑UE4 mannequin Init A pose↑
The model waistline was originally obliquely cut, and a significant portion of the animators mistakenly used it as a reference for pelvic rotation to flatten it causing the pelvis to actually tilt back severely.
Not all animators’ animations have this problem, but those that do are generally very cool from the presentation alone, and it would be a shame to not be able to use them for this reason.

↓I found a way to fix it↓
- Create a corrected initial pose for the UE4 mannequin skeleton currently being used for the problematic animation.
- Use this corrected initial pose to retarget the animation to the target skeleton.
As a result, the posture was corrected, although the legs and upper body were slightly misshapen.
Comparison of results
The picture may be corrected a little too much.
The IDLE animation is usually observed first.
The remaining problem is that repositioning the IK bones is troublesome because the usage of the IK bones differs from one animator to another.