Masked image with custom shader turns invisible on iOS

Hi!

I have a shader made by @pedroahpolonio that creates a blurred version of the background in a UI Image. I added a stencil to the shader to be able to mask the blurred image with a UI Mask (To be able to have the blur formed in any shape). Everything looks good within the editor but when I build to iOS the masked blur is not showing at all.

Here is the shader code:

 // Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'
 
 Shader "Unlit/FrostedGlassMaskable"
 {
     Properties
     {
         _Radius("Radius", Range(1, 255)) = 1
 
         // required for UI.Mask to work
          _StencilComp ("Stencil Comparison", Float) = 8
          _Stencil ("Stencil ID", Float) = 0
          _StencilOp ("Stencil Operation", Float) = 0
          _StencilWriteMask ("Stencil Write Mask", Float) = 255
          _StencilReadMask ("Stencil Read Mask", Float) = 255
          _ColorMask ("Color Mask", Float) = 15
          //
     }
 
     Category
     {
         Tags{ "Queue" = "Transparent" "IgnoreProjector" = "True" "RenderType" = "Opaque" }
 
         SubShader
         {
             GrabPass
             {
                 Tags{ "LightMode" = "Always" }
             }
 
             // required for UI.Mask to work
              Stencil
              {
                  Ref [_Stencil]
                  Comp [_StencilComp]
                  Pass [_StencilOp] 
                  ReadMask [_StencilReadMask]
                  WriteMask [_StencilWriteMask]
              }
               ColorMask [_ColorMask]
               //
 
             Pass
             {
                 Tags{ "LightMode" = "Always" }
 
                 CGPROGRAM
                 #pragma target 2.0
                 #pragma vertex vert
                 #pragma fragment frag
                 #pragma fragmentoption ARB_precision_hint_fastest
                 #include "UnityCG.cginc"
 
                 struct appdata_t
                 {
                     float4 vertex : POSITION;
                     float2 texcoord: TEXCOORD0;
                 };
 
                 struct v2f
                 {
                     float4 vertex : POSITION;
                     float4 uvgrab : TEXCOORD0;
                 };
 
                 v2f vert(appdata_t v)
                 {
                     v2f o;
                     o.vertex = UnityObjectToClipPos(v.vertex);
                     #if UNITY_UV_STARTS_AT_TOP
                     float scale = -1.0;
                     #else
                     float scale = 1.0;
                     #endif
                     o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
                     o.uvgrab.zw = o.vertex.zw;
                     return o;
                 }
 
                 sampler2D _GrabTexture;
                 float4 _GrabTexture_TexelSize;
                 float _Radius;
 
                 half4 frag(v2f i) : COLOR
                 {
                     half4 sum = half4(0,0,0,0);
 
                     #define GRABXYPIXEL(kernelx, kernely) tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx, i.uvgrab.y + _GrabTexture_TexelSize.y * kernely, i.uvgrab.z, i.uvgrab.w)))
 
                     sum += GRABXYPIXEL(0.0, 0.0);
                     int measurments = 1;
 
                     for (float range = 0.1f; range <= _Radius; range += 0.1f)
                     {
                         sum += GRABXYPIXEL(range, range);
                         sum += GRABXYPIXEL(range, -range);
                         sum += GRABXYPIXEL(-range, range);
                         sum += GRABXYPIXEL(-range, -range);
                         measurments += 4;
                     }
 
                     return sum / measurments;
                 }
                 ENDCG
             }
             GrabPass
             {
                 Tags{ "LightMode" = "Always" }
             }
 
             // required for UI.Mask to work
              Stencil
              {
                  Ref [_Stencil]
                  Comp [_StencilComp]
                  Pass [_StencilOp] 
                  ReadMask [_StencilReadMask]
                  WriteMask [_StencilWriteMask]
              }
               ColorMask [_ColorMask]
               //
 
             Pass
             {
                 Tags{ "LightMode" = "Always" }
 
                 CGPROGRAM
                 #pragma target 2.0
                 #pragma vertex vert
                 #pragma fragment frag
                 #pragma fragmentoption ARB_precision_hint_fastest
                 #include "UnityCG.cginc"
 
                 struct appdata_t
                 {
                     float4 vertex : POSITION;
                     float2 texcoord: TEXCOORD0;
                 };
 
                 struct v2f
                 {
                     float4 vertex : POSITION;
                     float4 uvgrab : TEXCOORD0;
                 };
 
                 v2f vert(appdata_t v)
                 {
                     v2f o;
                     o.vertex = UnityObjectToClipPos(v.vertex);
                     #if UNITY_UV_STARTS_AT_TOP
                     float scale = -1.0;
                     #else
                     float scale = 1.0;
                     #endif
                     o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
                     o.uvgrab.zw = o.vertex.zw;
                     return o;
                 }
 
                 sampler2D _GrabTexture;
                 float4 _GrabTexture_TexelSize;
                 float _Radius;
 
                 half4 frag(v2f i) : COLOR
                 {
 
                     half4 sum = half4(0,0,0,0);
                     float radius = 1.41421356237 * _Radius;
 
                     #define GRABXYPIXEL(kernelx, kernely) tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(float4(i.uvgrab.x + _GrabTexture_TexelSize.x * kernelx, i.uvgrab.y + _GrabTexture_TexelSize.y * kernely, i.uvgrab.z, i.uvgrab.w)))
 
                     sum += GRABXYPIXEL(0.0, 0.0);
                     int measurments = 1;
 
                     for (float range = 1.41421356237f; range <= radius * 1.41; range += 1.41421356237f)
                     {
                         sum += GRABXYPIXEL(range, 0);
                         sum += GRABXYPIXEL(-range, 0);
                         sum += GRABXYPIXEL(0, range);
                         sum += GRABXYPIXEL(0, -range);
                         measurments += 4;
                     }
 
                     return sum / measurments;
                 }
                 ENDCG
             }
         }
     }
 }

If I remove the UIMask, the blur is visible on an iOS device, so the blur shader works, It's just the masking part that makes it turn invisible.

Any suggestions on what to do to make this iOS/Android compatible?