gravity doesn't work in 4.9.1

I created physics assets for my character,in 4.8.3 everything works quite well,no matter in character BP and animation instance placed in the map.

but when I updated the engine to 4.9,the weird thing happened, when I place the character BP in the map and simulate or just play the character BP as the controlled pawn,it’s like no gravity is applied to the physics asset.
I take a screenshot and marked the difference between characterBP and animation instance while playing,the necklace part has physics as you can see the characterBp’s necklace is flying without gravity…

And today I updated to 4.9.1 nothing get better.So I have to use 4.8 until the problem get fixed.
Hope epic could fix this or tell me a way to solve this.
thanks very much.