Some people have reported to me that when they rotated the socket to a theoretically “wrong” rotation (eg. Z axis not pointig up), it worked. But these are cases in which only the aiming is misaligned, when in idle there’s no issue. If you are having issues even in idle, then it might be a different problem.
To find out, it would need to be tested in UE4 to see if happens too… but I suspect it’s some value under the hood that’s not applied until the editor is restarted.
It’s hard to know what’s going on under the hood in Unreal. I have some suggestions of things you can try to see if it goes away, like using the same skeleton for your characters (if they’re all using separate skeletons that are actually identical) - if the problem persists, at least you narrowed it down to specific animation sequences.
Another suggestion is (since it only happens when the IK nodes are connected) to go to a version of your character in which you didn’t add any part of my asset and test if using TwoBoneIK nodes on him will cause the issue.
None of these will guarantee that you’ll find the solution and it’s likely that the problem will persist for some of your animations or skeletons. And if you’d like a refund because of this, we can do that.