I have found the answer in this QA: Orientation Warping node not saving - #3 by DJ8189
And here is the issue list from unreal Engine: Unreal Engine Issues and Bug Tracker (UE-151538)
Just open the AnimationWarping.uplugin and set AnimationWarpingEditor’s LoadingPhrase to PreDefault will fix this problem.
And I also found this problem have been fixed at 5.1. The github fix list url can also found in issue list i have mentioned before.