Shader glitches object positions in WebGL DX11 but not DX9 GPU on DX11

This shows first in DX9, then in DX11 after the pause.

I have used a slightly modified shader from here:
http://www.shaderslab.com/demo-77---cel-shading-(formula).html

With no emulation, it becomes a glitchy mess, but in WebGL1.0 emulation, it is fine. I am new to shading and I don't understand why this is happening...

Here is the shader code:

Code (CSharp):

1. Shader "Toon/Lighting/CelShader"
2. {
3.     Properties
4.     {
5.         _MainTex ("Texture", 2D) = "white" {}
6.         _Treshold ("Cel treshold", Range(1., 20.)) = 5.
7.         _Ambient ("Ambient intensity", Range(0., 0.5)) = 0.1
8.     }
9.     SubShader
10.     {
11.         Tags
12.         {
13.             "RenderType"="Opaque"
14.             //"LightMode"="ForwardBase"
15.         }
16.  
17.         LOD 200
18.         Cull Back
19.         Pass
20.         {
21.             CGPROGRAM
22.             #pragma vertex vert
23.             #pragma fragment frag
24.             #pragma multi_compile_instancing
25.          
26.             #include "UnityCG.cginc"
27.             sampler2D _MainTex;
28.  
29.             UNITY_INSTANCING_BUFFER_START(Props)
30.                 UNITY_DEFINE_INSTANCED_PROP(fixed, _Treshold)
31.                 UNITY_DEFINE_INSTANCED_PROP(fixed, _Ambient)
32.             UNITY_INSTANCING_BUFFER_END(Props)
33.  
34.             fixed4 _MainTex_ST;
35.             fixed4 _LightColor0;
36.  
37.             struct v2f
38.             {
39.                 float4 pos : SV_POSITION;
40.                 float2 uv : TEXCOORD0;
41.                 float3 worldNormal : NORMAL;
42.             };
43.             float LightToonShading(float3 normal, float3 lightDir)
44.             {
45.                 fixed treshold = UNITY_ACCESS_INSTANCED_PROP(Props, _Treshold);
46.  
47.                 fixed NdotL = max(0.0, dot(normalize(normal), normalize(lightDir)));
48.                 return floor(NdotL * treshold) / (treshold - 0.5);
49.             }
50.             v2f vert (appdata_base v)
51.             {
52.                 v2f o;
53.                 o.pos = UnityObjectToClipPos(v.vertex);
54.                 o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
55.                 o.worldNormal = UnityObjectToWorldNormal(v.normal);
56.                 return o;
57.             }
58.             fixed4 frag (v2f i) : SV_Target
59.             {
60.                 fixed4 col = tex2D(_MainTex, i.uv);
61.                 col.rgb *= saturate(LightToonShading(i.worldNormal, _WorldSpaceLightPos0.xyz) + UNITY_ACCESS_INSTANCED_PROP(Props, _Ambient)) * _LightColor0.rgb;
62.                 return col;
63.             }
64.             ENDCG
65.         }
66.     }
67. }

I am almost sure there is a really simple solution to this that I have overlooked. Please help me if you can.