worldPos not correct in surface shader

Hello!

I am writing a custom Unity Shader where the mesh data is constructed in a Compute Shader and then drawn using Graphics.DrawProceduralIndirect.

The problem I have is, that the shader I want to write needs the worldPos of the current fragment, but when visualizing the worldPos it is always (1, 0, 0). I have checked the generated Shader code and what I understand it seems to be not properly set. The x-component is the only component which is assigned to 1:

 // fragment shader
 fixed4 frag_surf_shader (v2f_surf_shader IN) : SV_Target {
   UNITY_SETUP_INSTANCE_ID(IN);
   // prepare and unpack data
   Input surfIN;
   #ifdef FOG_COMBINED_WITH_TSPACE
     UNITY_EXTRACT_FOG_FROM_TSPACE(IN);
   #elif defined FOG_COMBINED_WITH_WORLD_POS
     UNITY_EXTRACT_FOG_FROM_WORLD_POS(IN);
   #else
     UNITY_EXTRACT_FOG(IN);
   #endif
   UNITY_INITIALIZE_OUTPUT(Input,surfIN);
   surfIN.col.x = 1.0;
   surfIN.worldPos.x = 1.0;
   surfIN.col = IN.custompack0.xyzw;
   float3 worldPos = IN.worldPos.xyz;
   #ifndef USING_DIRECTIONAL_LIGHT
     fixed3 lightDir = normalize(UnityWorldSpaceLightDir(worldPos));
   #else
     fixed3 lightDir = _WorldSpaceLightPos0.xyz;
   #endif
   #ifdef UNITY_COMPILER_HLSL
   SurfaceOutput o = (SurfaceOutput)0;
   #else
   SurfaceOutput o;
   #endif
   o.Albedo = 0.0;
   o.Emission = 0.0;
   o.Specular = 0.0;
   o.Alpha = 0.0;
   o.Gloss = 0.0;
   fixed3 normalWorldVertex = fixed3(0,0,1);
   o.Normal = IN.worldNormal;
   normalWorldVertex = IN.worldNormal;
 
   // call surface function
   surf_shader (surfIN, o);

And this is the original shader:

 Shader "Game/Map Shader" {
     Properties
     {
         _MainTex ("Texture", 2D) = "white" {}
     }
     SubShader {
         LOD 200
         Tags {"RenderType"="Opaque" }
         
         CGPROGRAM
         #include "UnityCG.cginc"
         #include "MapShared.cginc"
         
         #pragma target 4.5  
         #pragma surface surf_shader Lambert vertex:vertex_shader addshadow fullforwardshadows 
 
         #ifdef SHADER_API_D3D11
         StructuredBuffer<RenderData> renderData;
         #endif
         
         struct Input {
             float3 worldPos;
         };
         
         struct appdata_id
         {
             float4 vertex : POSITION;
             float3 normal : NORMAL;
             float4 texcoord : TEXCOORD0;
             
             uint id : SV_VertexID;
                     uint inst : SV_InstanceID;
         };
 
         void vertex_shader(inout appdata_id v, out Input i)
         {
             #ifdef SHADER_API_D3D11
             UNITY_INITIALIZE_OUTPUT(Input,i); 
             
             RenderData rd = renderData[v.id];
             v.vertex = float4(rd.position.xyz, 1.0f);
             v.normal = normalize(mul(float4(rd.normal.xyz, 0.0), unity_WorldToObject).xyz);
             #endif
         }
         
         void surf_shader(Input IN, inout SurfaceOutput o)
         {
             #ifdef SHADER_API_D3D11
             o.Albedo = float4(clamp(abs(IN.worldPos.xyz),0,1), 1.0f);
             #endif
         }
         ENDCG
     }
 }

Does anyone have an idea why this happens? I would really appreciate it if anyone could point me into the right direction.