Shader normals modification different in build

I'm using a render texture for a glow effect around contact between characters and floor. Works great in the editor, but when I build the texture isn't displaying properly, the mapping is shifted, and I think the clipping planes are different. Any ideas?

Here's the desired effect in the editor on the left, problematic build on the right:

Here I modified the texture to show the problem better... notice it's shifted down (the fact that it's solid color and maybe the fact that it's smaller is the clipping planes not being the same as the editor)

EDIT: I narrowed it down. I'm using SetReplacementShader for the render texture camera, and in the replacement shader I'm inflating the meshes along their normals in vert with: "v.vertex.xyz += (v.normal * _Bloat) ;" this works in the editor, but in the build it just pushes them to one side... here's my shader code... does anyone know why this would be?

 Shader "Custom/Disco Floor Mask" {
     Properties {
         _Bloat("Bloat Geo", Range(0, 1)) = 0.025
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         
         Pass {
             Cull Off
 
             CGPROGRAM
                 #pragma vertex vert
                 #pragma fragment frag
                 #include "UnityCG.cginc"
 
                 struct v2f {
                     half4 pos : POSITION;
                 };
                 
                 float _Bloat;
                 v2f vert(appdata_base v) {
                     v2f o;
                     v.vertex.xyz += (v.normal * _Bloat) ; // bump the normals out a bit
                     o.pos = mul(UNITY_MATRIX_MVP, v.vertex) ;
                     return o;
                 }
                 
                 
                 float4 frag(v2f IN) : COLOR {
                     return half4(1,1,1,1);
                 }
             ENDCG
         }
     }
 }