VertexLit Hilight Shader - Flicker on iOS Problem

Hi everyone! I'm pretty new to shader coding, but I managed to hack together a Hilight Shader that uses the Mobile VertexLit as its core, plus the outline code from Toon Basic Outline (both of these are builtin shaders).

BUT, the outline "higlight" is flickering on iOS devices. Could someone who is wise to shaders please take a look at this short shader and tell me why I'd be getting a flicker please? Thank you!

 // Mobile VertexLit PLUS highlight outline
 Shader "Custom/Mobile VertexLit Hilight" {
 
     Properties {
         _MainTex ("Base (RGB)", 2D) = "white" { }
     }
 
     CGINCLUDE
     #include "UnityCG.cginc"
     
     struct appdata {
         half4 vertex : POSITION;
         float3 normal : NORMAL;
     };
 
     struct v2f {
         half4 pos : POSITION;
         half4 color : COLOR;
     };
         
     // Outline relative to camera distance. See standard Toon Basic Outline shader for non-relative version
     v2f vert(appdata v) {
         v2f o;
         o.pos = v.vertex;
         o.pos.xyz += v.normal.xyz * 0.0225;//_Outline
         o.pos = mul(UNITY_MATRIX_MVP, o.pos);
         o.color.r = 0; //0
         o.color.g = 0.377; //96
         o.color.b = 1; //255
         return o;
     }
 
     ENDCG
 
     SubShader {
         Tags { "RenderType"="Opaque" }
         UsePass "Custom/Mobile VertexLit Named/BASIC"
         Pass {
             Name "OUTLINE"
             Tags { "LightMode" = "Always" } //"Vertex" }
             Cull Front
             ZWrite On
             ColorMask RGB
             Blend SrcAlpha OneMinusSrcAlpha
 
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             half4 frag(v2f i) :COLOR { return i.color; }
             ENDCG
         }
     }
 
     Fallback "Mobile/VertexLit"
 }