Background camera flicker AR Foundation

[jalajshah]

Hello every one ,
Unity Version : 2019.3.1f
AR Foundation 2.1.4

i am working on AR Portal project :
Model poly count : 240k , batches : 75, verts 105k , set pass call 75

getting 200+ fps in editor , 60 around fps in iphone XR+ device
but 20-40 fps in other iPhone device

i had done all thing what i know , still not getting any solution.

[jalajshah]

Here is my profiler , but i cant understand what is issue. !!

[jalajshah]

Editor running test.

[jalajshah]

three different device testing screenshot