WebGL displacement shader doesn't work in build

I'm working on a displacement and tessellation shader for a WebGL project. I have isolated it as the main reason why the build doesn't work but don't know why it doesn't work. Here is the shader itself:

 Shader "Custom/Digsite_v2"
 {
     Properties
     {
         _Tess ("Tesselation", Range(1,32)) = 4
         _Color ("Soil", Color) = (1,1,1,1)
         _SoilTex("Soil (RGB)", 2D) = "white" {}
         _GroundColor("Ground", Color) = (1,1,1,1)
         _GroundTex("Ground (RGB)", 2D) = "white" {}
         _Splat("Splat Map", 2D) = "black"{}
         _Displacement("Displacement", Range(0,1.0)) = 0.3
         _Glossiness ("Smoothness", Range(0,1)) = 0.5
         _Metallic ("Metallic", Range(0,1)) = 0.0
     }
     SubShader
     {
         Tags { "RenderType"="Opaque" }
         LOD 200
 
         CGPROGRAM
         // Physically based Standard lighting model, and enable shadows on all light types
         #pragma surface surf Standard fullforwardshadows vertex:disp tessellate:tessFixed
         #pragma target 4.6
         #include "Tessellation.cginc"
         struct appdata {
                 float4 vertex : POSITION;
                 float4 tangent : TANGENT;
                 float3 normal : NORMAL;
                 float2 texcoord : TEXCOORD0;
             };
         
         float _Tess;
 
         float4 tessFixed()
         {
             return _Tess;
         }
 
         sampler2D _Splat;
         float _Displacement;
 
         void disp(inout appdata v)
         {
             float d = tex2Dlod(_Splat, float4(v.texcoord.xy,0,0)).r * _Displacement;
             v.vertex.xyz -= v.normal * d;
             //v.vertex.xyz += v.normal * _Displacement;
         }
         sampler2D _GroundTex;
         fixed4 _Color;
         sampler2D _SoilTex;
         fixed4 _GroundColor;
 
         struct Input
         {
             float2 uv_GroundTex;
             float2 uv_SoilTex;
             float2 uv_Splat;
         };
 
         half _Glossiness;
         half _Metallic;
 
         // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
         // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
         // #pragma instancing_options assumeuniformscaling
         UNITY_INSTANCING_BUFFER_START(Props)
             // put more per-instance properties here
         UNITY_INSTANCING_BUFFER_END(Props)
 
         void surf (Input IN, inout SurfaceOutputStandard o)
         {
             // Albedo comes from a texture tinted by color
             half amount = tex2Dlod(_Splat, float4(IN.uv_Splat, 0, 0)).r;
             fixed4 c = lerp(tex2D(_GroundTex, IN.uv_GroundTex) * _GroundColor, 
                 tex2D(_SoilTex, IN.uv_SoilTex) * _Color, amount);
             //fixed4 c =  tex2D (_MainTex, IN.uv_MainTex) * _Color;
             o.Albedo = c.rgb;
             // Metallic and smoothness come from slider variables
             o.Metallic = _Metallic;
             o.Smoothness = _Glossiness;
             o.Alpha = c.a;
         }
         ENDCG
     }
     FallBack "Diffuse"
 }