Iphone X having weird spike performance in profiler while iphone 6 works fine

I built my game into iphone X using latest Xcode and iOS 11.2 in unity version 2017.2.0p1. However, I just notice there is this weird performance spike comes out when iphone X runs my game for a while and it is pretty consistent even after I restart my game. I believe that happens when Iphone X is hot after running for a bit. While I tried same build on iphone 6, no such spike. My iphone 6 is using iOS 11 instead of 11.2.
The spike in profiler is following:
Animator.Update
>Animator.DirtySceneObjects -------------------------> this is the one that causing the spike
>WaitforJobgroup

I am not sure what is going on as it was working fine in my iphone 6. Does anyone else experiencing same problem?