I have been experiencing this myself, but just while using CC3 and Unreal.

I transferred same motions from CC3 3.22 to Unreal 4.24.3, while using 2 characters loaded in CC3 at the time export:
(1) CC3 Default
(2) CC3 Headshot 

I am finding that I will experiencing the above issue if I transfer animations out with opposing character.
If I export out while CC3-Default is the loaded in CC3, it looks fine on CC3-Default mesh in Unreal...but then when applied to the Headshot mesh in Unreal, eyes and teeth are out of place.
Likewise, if I transfer out while Headshot is loaded in CC3, it looks fine on the Headshot mesh in Unreal...but then when applied to the CC3-Default mesh in Unreal, eyes and teeth are out of place.

Now, I can apply motions universally to iClone on both characters, and there are no issues with teeth or eyes in iClone.

 So, it appears it is on the Unreal end of things - somewhere in the export-import process, the (a) teeth and (b) eye bones are permanently matched to the exported character's eye and teeth location.  Like it is 'baked' to the exported mesh size.  So, then when the motion is applied to another sized mesh in Unreal, the eyes and teeth are out of place.  You would never notice this if the avatars so happen to have identical-positioned and identical-shaped heads.  But if they are different, then it will present.

Additionally, in my case, the difference of the eyes and teeth issue exactly correlated to the difference in the meshes:
My Headshot has a more raised and back head, so on the CC3-Default in UE4, the eyes and teeth from a Headshot exported animations has higher eyes (teeth are probably further behind face).
Likewise, my CC3-Default correspondingly has a more lowered and forward head, so on the Headshot in UE4, the eyes and teeth from a CC3-Default exported animation has lower eyes and protruding teeth.

Basically, team needs to fix so skeleton location of eyes and teeth is not 'baked' into an animation.  Then you could apply an animation to any character once in UE4.  Otherwise, you would need to export out with that said character so that the eyes and teeth are located properly in UE4.

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我本人一直在经历这种情况，只是在使用CC3和Unreal时。

我将相同的动作从CC3 3.22转移到了Unreal 4.24.3，同时在导出时使用了CC3中加载的2个字符：
（1）CC3默认
（2）CC3头像

我发现如果我以相反的角色转出动画，将会遇到上述问题。
如果在CC3中加载了CC3-Default的情况下导出时，在Unreal中的CC3-Default网格上看起来还不错...但是，当将其应用于Unreal中的Headshot网格时，眼睛和牙齿都不合适。
同样，如果我在Headshot加载到CC3中时转移出去，它在Unreal中的Headshot网格上看起来还不错……但是当应用于Unreal中的CC3-Default网格时，眼睛和牙齿都不合适。

现在，我可以将动作普遍应用于两个角色的iClone，并且iClone中的牙齿或眼睛没有问题。

 因此，这似乎是虚幻的结果-在进出口过程中的某处，（a）牙齿和（b）眼骨与出口角色的眼睛和牙齿位置永久匹配。就像它被“烘焙”到导出的网格尺寸一样。因此，当将运动应用于“虚幻”中的另一个尺寸的网格时，眼睛和牙齿就不正确了。如果化身恰好具有相同位置和相同形状的头部，您将永远不会注意到这一点。但是，如果它们不同，那么它将呈现。

另外，在我的情况下，眼睛和牙齿的差异与网格的差异完全相关：
我的爆头具有更高的抬头和后脑，因此在UE4中的CC3-Default上，爆头导出的动画的眼睛和牙齿的眼睛更高（牙齿可能位于面部的后面）。
同样，我的CC3-Default相应地具有更低的头部和向前的头部，因此在UE4中的“爆头”中，CC3-Default导出的动画的眼睛和牙齿具有较低的眼睛和突出的牙齿。

基本上，团队需要修复，以便眼睛和牙齿的骨骼位置不会“烘焙”到动画中。然后，您可以在UE4中一次将动画应用于任何角色。否则，您需要导出带有该字符的字符，以便在UE4中正确放置眼睛和牙齿。


THX!

Still having the issue. It appears on Blender when importing a file exported to Unreal.

And when happens too when I try to use the same skeleton for multiple exported characters in Unreal (so they can share the same animations)

Tested in 3.22 too, same problem...