Screen Space Ambient Occlusion Issues
You need to be careful about spaces - position and normal need to be in view space.

To transform depth into view space position I used this method.
So:

vec3 viewPositionFromDepth(vec2 vTexCoord)
{
    float z = texture2D(depthTexture, vTexCoord).r;
    // Get x/w and y/w from the viewport position
    float x = vTexCoord.x * 2.0 - 1.0;
    float y = vTexCoord.y * 2.0 - 1.0;
    vec4 vProjectedPos = vec4(x, y, z, 1.0f);
    // Transform by the inverse projection matrix
    vec4 vPositionVS = invProjection*vProjectedPos;
    // Divide by w to get the view-space position
    return vPositionVS.xyz / vPositionVS.w;
}


To transform normal into view space you need to multiply it by transpose of inverse of view matrix (should be done on CPU):

vec4 n = transpose(inverse(ViewMatrix)) * normalize(texture2D(normalTexture, texCoord)*2.0 - 1.0 );


And in loop while sampling depth with offset to compare with kernel position, this depth should be in same space as position so I did it the same way:

float sampleDepth = viewPositionFromDepth(offset.xy).z;


This is not the most optimal way though, but it worked for me.