Custom shader always reverts to fallback

Hi,

I have a custom shader that's basically a copy of Unity's built-in Transparent/Diffuse at this moment:

 Shader "Custom/TransparentDiffuseSaturation" {
 Properties {
     _Color ("Main Color", Color) = (1, 1, 1, 1)
     _MainTex ("Base (RGB)", 2D) = "white" {}
 }
 
 SubShader {
     Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
     LOD 200
 
 CGPROGRAM
 #pragma surface surf Lambert alpha
         
 sampler2D _MainTex;
 fixed4 _Color;
         
 struct Input {
     float2 uv_MainTex;
 };
         
 void surf (Input IN, inout SurfaceOutput o) {
     fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
     o.Albedo = c.rgb;
     o.Alpha = c.a;
 }
 ENDCG
 } 
 
 Fallback "Diffuse"
 }

It works fine in the editor view, but only if the game is not running. As soon as I click "Play", it reverts to the Fallback shader. Same thing happens in web and standalone builds.

The funny thing is, if I set Fallback to Transparent/Diffuse, it actually does fall back to Transparent/Diffuse. It looks like for some reason it just won't execute the SubShader code.

What should I do to make it work?