BUGGY, unintentional flickering light on material when hit with spotlight

BUGGY, unintentional flickering light on material when hit with spotlight.

I am using the "Transparent/Diffuse ZWrite" shader pulled verbatim from the current Unity docs which worked perfectly for fading out objects between the player and the camera until I upgraded to Unity 5.6.

Ever since I upgraded to v5.6, I get constant light flickering on my object's once GI is baked (with AO), when fully opaque - it is an constant flicker. I have tried everything I can think of to eliminate this with zero resolution - any ideas?

Shader code:
(pulled from https://docs.unity3d.com/Manual/SL-CullAndDepth.html)

Shader "Transparent/Diffuse ZWrite" {
Properties {
_Color ("Main Color", Color) = (1,1,1,1)
_MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
}
SubShader {
Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
LOD 200

// extra pass that renders to depth buffer only
Pass {
ZWrite On
ColorMask 0
}

// paste in forward rendering passes from Transparent/Diffuse
UsePass "Transparent/Diffuse/FORWARD"
}
Fallback "Transparent/VertexLit"
}