On android texture is degrading after multiple writings, but on PC it's ok

Here are images before and after 100x writes:

Before <-|-> After

Texture is RenderTexture ARGB32.
Bug only occurs on android, on PC it works flawless.

Anyone know what is going on?

Some of the relevant code:

public void Draw ( Material drawingMat )
    drawingMat.SetTexture(_MainTexID, pingPongRts[0]);

    tmpRenderTexture = RenderTexture.active;
    RenderTexture.active = pingPongRts[1];
    GL.Clear(true, true, Color.magenta);
    Graphics.DrawMeshNow(mesh, transform.localToWorldMatrix);

    RenderTexture.active = tmpRenderTexture;


    Graphics.CopyTexture(pingPongRts[0], output);

void Swap<T>(T[] array)
    var tmp = array[0];
    array[0] = array[1];
    array[1] = tmp;