Graphics.DrawTexture with multiple camera on mobile device not working

Hi, I'm working on a project that needs to use multiple cameras with fisheye effect from the standard assets., and draw it on an external display.
At first I tried to use Graphics.Blit(), but Camera.SetTargetBuffer(Display.displays[1].color /depthbuffer) doesn't work with post effect shaders(OnRenderImage()).

I found the method Graphics.DrawTexture() which can draw on a specific region of a RenderTexture. And it works well on the editor with multiple cameras with fisheye shader.

So I created a rendertexture, put it on a quad, and put a default camera looking at it. and when there is an external display, I changed the camera's targetbuffers to those of the external display.

It works perfect in the editor, but when I build it on my device(ios) it doesn't work. Only one camera renders to the rendertexture. I tried changing quality settings but no work.

Is there a limit with Graphics.DrawTexture on a mobile devices? On standalone it works just perfect. Or, are you guys have any better suggestion?