Unity UI + RenderTexture broken since 5.0.1p4

In our project one of the scenes we use a Camera with some sprites and a Canvas set to Screen Space - Camera. The contents of the camera is rendered into a RenderTexture that is put onto a procedural mesh and another main camera sees that mesh.
We call the Camera.Render() in LateUpdate to render the texture. Until 5.0.1p3 this works fine. (Except an already known bug: it has to be rendered twice to get the UI elements properly. Any ideas when that will be fixed?)
However the main problem is that after 5.0.1p4 the UI elements doesn’t get rendered to the texture at all. They are shown properly in the scene view but they are somehow not in the rendering pipeline anymore. Tried to call the Render() method in normal Update, or yield until WaitForEndOfFrame and call it there. Tried OnPreRender, OnPostRender whatever I could find, but nothing.
We are stuck and cannot upgrade any further (no fix so far in the upcoming versions).
Any ideas what might have caused this? I don’t see any rendering core or UI related change in the 5.0.1p4 changelog.
Shall I file a bug report or is this a known problem?

Have you tried simply setting the camera which renders to the texture to have a lower (numerically) Camera Depth? This will force it to be rendered by the normal rendering chain prior to rendering the camera that should see the rendered texture.

This has been working for me.

I filed a bug. Until it is resolved if anyone knows a temporary workaround, let me know!

This is a known issue with Unity. You can find more details at:

https://forum.unity3d.com/threads/rendertexture-not-working-on-ios-and-android-unity-4-2-0f4.192561/

https://forum.unity3d.com/threads/render-texture-not-working-on-device-unity-5-2-1f1.358483/

https://forum.unity3d.com/threads/render-texture-works-in-editor-but-not-on-devices-after-upgrade-to-unity-5.362397/

and a few others where the moderators and staff claim it is fixed in a future release or (with a touch of unnecessary arrogance) that the issue is the user and a bug never existed at all.

BUT

This is going to sound silly, but add an ImageEffect to the main camera. I have made a dummy effect that is attached to my main camera and without any logical explanation, it fixes RenderTexture on mobile.

DummyEffect.cs:

using UnityEngine;

[ExecuteInEditMode]
[AddComponentMenu("Image Effects/Dummy Effect")]
public class DummyEffect : ImageEffectBase {

	// Called by camera to apply image effect
	void OnRenderImage (RenderTexture source, RenderTexture destination) {
		Graphics.Blit (source, destination, material);
	}
}

DummyEffect.shader:

Shader "Hidden/Dummy Effect" {
Properties {
	_MainTex ("Base (RGB)", RECT) = "white" {}
}

SubShader {
	Pass {
		ZTest Always Cull Off ZWrite Off
		Fog { Mode off }

CGPROGRAM
#pragma vertex vert_img
#pragma fragment frag
#pragma fragmentoption ARB_precision_hint_fastest
#include "UnityCG.cginc"

uniform sampler2D _MainTex;

float4 frag (v2f_img i) : COLOR {
	return tex2D(_MainTex, i.uv);
}
ENDCG

	}
}

Fallback off

}