Shader behaves differently on tvOS (Apple TV)

Unity Engine
,
1

I’ve got a shader of 2d water with a foam. Nothing fancy or super complex.
However I was unpleasantly surprised when I launched the game on tvOS: the shader was definitely working incorrectly since the water had to much foam.
5309679--533715--upload_2019-12-23_17-35-53.png
Here is an abstract of the fragment shader responsible for the foam

fixed4 frag(v2f IN) : SV_Target
{
    half2 dist1 = tex2D( _DistMap, IN.uvdist1 ).rg;
    half2 dist2 = tex2D( _DistMap, IN.uvdist2 ).rg;
    half2 dist = lerp(dist1, dist2, _DetailInfluence) * 2.0 - 1.0;

    fixed wave = sqrt(saturate(dist.x * dist.y));
    fixed foam = step(_WaveFoam, wave);
    fixed4 foamColor = fixed4(foam.xxx * _WaveFoamAlpha, 0.0);
    ...
    fixed4 color = tex2D( _ReflMap, reflUV );
    ...
    color += waveCrestColor;
    return saturate(color);
}

My first thought was about precision. I tried changing fixed to half, but it made no change.
Also I had no saturate inside sqrt before, but it made no changes too.
Any ideas why Apple TV’s PowerVR runs my shader this way?

2

Actually it appeared the saturate inside sqrt indeed solved the problem.