Bug Get the ARCamera image to a RenderTexture, ReadPixels from the RenderTexture then set to a RawImage

Unity Version : Unity2020.3.18
ARFoundation Version : 4.2.1
ARCore XR Plugin 4.2.1
Platform : Android

I Get the ARCamera Image Real-time, Render to a RenderTexture, then ReadPixels from the RenderTexture ,and set to a RawImage , unfortunately, the RawImage flickers color .

follow is my code:

Code (CSharp):

1. public Camera cam;
2. public RawImage img;
3.  
4. private Texture2D renderResult = null;
5.  
6. public RenderTexture camRT;
7.  
8. #region GPU
9.  
10. private RenderTexture mRenderTexture;
11.  
12. private void Update()
13. {
14.    if (mRenderTexture == null)
15.    {
16.        RenderTextureDescriptor renderTextureDes = new RenderTextureDescriptor(480, 640, RenderTextureFormat.BGRA32);
17.  
18.        mRenderTexture = RenderTexture.GetTemporary(renderTextureDes);
19.    }
20.  
21.    cam.targetTexture = mRenderTexture;
22.    cam.Render();
23.  
24.    RenderTexture.active = mRenderTexture;
25.  
26.    if (renderResult == null)
27.        renderResult = new Texture2D(480, 640, TextureFormat.RGB24, false);
28.  
29.    renderResult.ReadPixels(new Rect(0, 0, mRenderTexture.width, mRenderTexture.height), 0, 0);
30.    renderResult.Apply();
31.  
32.    img.texture = renderResult;
33.  
34.    cam.targetTexture = null;
35.    RenderTexture.active = null;
36.  
37. }
38.  
39. #endregion

it like flicker every few frames . It's too strange . and it works fine on ios devices. just error on android devices . has anyone had this problem? and how to solve this problem?

i take some photos :