It's June 2017 and I'm still getting the same error as everyone else on Unity 5.5.3f1 with an iPhone 6S. I have to use diffuse mobile errors to get good performance out of the game.

Here's the error:

-------- Shader compilation failed
#version 100
#extension GL_EXT_frag_depth : enable
precision highp float;
uniform highp vec4 _ProjectionParams;
uniform highp vec4 _ZBufferParams;
uniform highp mat4 unity_CameraToWorld;
uniform highp mat4 _NonJitteredVP;
uniform highp mat4 _PreviousVP;
uniform highp sampler2D _CameraDepthTexture;
varying highp vec2 xlv_TEXCOORD0;
varying highp vec3 xlv_TEXCOORD1;
void main ()
{
highp vec4 tmpvar_1;
tmpvar_1 = texture2D (_CameraDepthTexture, xlv_TEXCOORD0);
mediump vec2 tmpvar_2;
highp vec4 tmpvar_3;
tmpvar_3.w = 1.0;
tmpvar_3.xyz = ((xlv_TEXCOORD1 * (_ProjectionParams.z / xlv_TEXCOORD1.z)) * (1.0/((
(_ZBufferParams.x * tmpvar_1.x)
+ _ZBufferParams.y))));
highp vec4 tmpvar_4;
tmpvar_4 = (unity_CameraToWorld * tmpvar_3);
highp vec4 tmpvar_5;
tmpvar_5 = (_PreviousVP * tmpvar_4);
highp vec4 tmpvar_6;
tmpvar_6 = (_NonJitteredVP * tmpvar_4);
highp vec2 tmpvar_7;
tmpvar_7 = (((tmpvar_5.xy / tmpvar_5.w) + 1.0) / 2.0);

highp vec2 tmpvar_8;
tmpvar_8 = (((tmpvar_6.xy / tmpvar_6.w) + 1.0) / 2.0);
tmpvar_2 = (tmpvar_8 - tmpvar_7);
mediump vec4 tmpvar_9;
tmpvar_9.zw = vec2(0.0, 1.0);
tmpvar_9.xy = tmpvar_2;
gl_FragDepthEXT = tmpvar_1.x;
gl_FragData[0] = tmpvar_9;
}

THIS IS NOT RESOLVED. GOT THE SAME ERROR!

The error log is:
WARNING: 0:4: extension 'GL_EXT_frag_depth' is not supported
ERROR: 0:38: Use of undeclared identifier 'gl_FragDepthEXT'

Note: Creation of internal variant of shader 'Hidden/Internal-MotionVectors' failed.
WARNING: Shader Unsupported: 'Hidden/Internal-MotionVectors' - Pass '' has no vertex shader
WARNING: Shader Unsupported: 'Hidden/Internal-MotionVectors' - Setting to default shader.
WARNING: Shader Unsupported: 'Hidden/VR/BlitCopyFromTexArray' - Pass '' has no vertex shader
WARNING: Shader Unsupported: 'Hidden/VR/BlitCopyFromTexArray' - Setting to default shader.

This is happening to me in 5.6.0f1, in iOS and Android.

OPENGL LOG: Creating OpenGL ES 2.0 graphics device ; Context level <OpenGL ES 2.0> ; Context handle 392377776
Initialize engine version: 5.5.1p1 (d7332d2a7307)
-------- Shader compilation failed
#version 100
#extension GL_EXT_frag_depth : enable
precision highp float;
uniform highp vec4 _ProjectionParams;
uniform highp vec4 _ZBufferParams;
uniform highp mat4 unity_CameraToWorld;
uniform highp mat4 _NonJitteredVP;
uniform highp mat4 _PreviousVP;
uniform highp sampler2D _CameraDepthTexture;
varying highp vec2 xlv_TEXCOORD0;
varying highp vec3 xlv_TEXCOORD1;
void main ()
{
highp vec4 tmpvar_1;
tmpvar_1 = texture2D (_CameraDepthTexture, xlv_TEXCOORD0);
mediump vec2 tmpvar_2;
highp vec4 tmpvar_3;
tmpvar_3.w = 1.0;
tmpvar_3.xyz = ((xlv_TEXCOORD1 * (_ProjectionParams.z / xlv_TEXCOORD1.z)) * (1.0/((
(_ZBufferParams.x * tmpvar_1.x)
+ _ZBufferParams.y))));
highp vec4 tmpvar_4;
tmpvar_4 = (unity_CameraToWorld * tmpvar_3);
highp vec4 tmpvar_5;
tmpvar_5 = (_PreviousVP * tmpvar_4);
highp vec4 tmpvar_6;
tmpvar_6 = (_NonJitteredVP * tmpvar_4);
highp vec2 tmpvar_7;
tmpvar_7 = (((tmpvar_5.xy / tmpvar_5.w) + 1.0) / 2.0);
highp vec2 tmpvar_8;
tmpvar_8 = (((tmpvar_6.xy / tmpvar_6.w) + 1.0) / 2.0);
tmpvar_2 = (tmpvar_8 - tmpvar_7);
mediump vec4 tmpvar_9;
tmpvar_9.zw = vec2(0.0, 1.0);
tmpvar_9.xy = tmpvar_2;
gl_FragDepthEXT = tmpvar_1.x;
gl_FragData[0] = tmpvar_9;
}
-------- failed compiling:
fragment evaluation shader
WARNING: 0:4: extension 'GL_EXT_frag_depth' is not supported
ERROR: 0:38: Use of undeclared identifier 'gl_FragDepthEXT'

Note: Creation of internal variant of shader 'Hidden/Internal-MotionVectors' failed.
WARNING: Shader Unsupported: 'Hidden/Internal-MotionVectors' - Pass '' has no vertex shader
WARNING: Shader Unsupported: 'Hidden/Internal-MotionVectors' - Setting to default shader.

Still occurs in Unity 5.5.0f3 when building for android, could this cause this glitch? https://pbs.twimg.com/media/Czd5wX2XcAE9Sk-.jpg I was looking through the adb logcat for hints to this glitch and found this issuetracker

Still having the issue with 5.4.2f2.

This is not fixed in 5.4.3f1. I'm getting the same error as everyone else.

Still a problem in 5.4.2f2!!

Still same problem in Unity 5.4.2f2 , using MacOS El Sierra here.
Have this problem on

iPad mini (iOS 9.3.5) and
iPad Air 2, (iOS 9.3.5)
iPhone6 , (iOS 10.1.1)