Phong lighting leaves stripes pattern - c++

Question

I am learning lighting on OpenGL, in this example, I used the phong method. Everything seems to be working as intended, but I notice that this method leaves some "stripes", especially in the diffuse part of the resulting color:
Vertex shader:
#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 normal;
struct Light{
vec3 position;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
uniform mat4 Model;
uniform mat4 View;
uniform mat4 Projection;
uniform Light light;
out vec3 aNormal;
out vec3 FragPos;
out vec3 LightPos;
//Usually you would transform the input into coordinates that fall within OpenGL's visible region
void main()
{
aNormal = mat3(transpose(inverse(View * Model))) * normal;
FragPos = vec3(View * Model * vec4(aPos,1.0));
gl_Position = Projection * vec4(FragPos,1.0);
LightPos = vec3(View * vec4(light.position,1.0));
}
#version 330 core
out vec4 FragColor;
in vec3 aNormal;
in vec3 FragPos;
in vec3 LightPos;
struct Material{
vec3 ambient;
vec3 diffuse;
vec3 specular;
float shininess;
};
struct Light{
vec3 position;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
uniform Material material;
uniform Light light;
precision highp float;
void main()
{
vec3 ambient = material.ambient * light.ambient;
vec3 norm = normalize(aNormal);
//Difuse
vec3 lightDir = normalize(LightPos - FragPos);
float diff = max(dot(norm,lightDir),0.0);
vec3 diffuse = (diff * material.diffuse) * light.diffuse;
vec3 specular = vec3(0);
//Specular
if(diff > 0){
vec3 viewDir = normalize(-FragPos);
vec3 reflectDir = reflect(-lightDir,norm);
float spec = pow(max(dot(viewDir,reflectDir),0.0), material.shininess);
specular = light.specular * (spec * material.specular);
}
vec3 result = diffuse + (ambient + specular);
FragColor = vec4(result, 1.0);
}
Fragment shader:
I was wondering why that happens, I have a suspicion that is related to float precision, however I tried to use precision highp float; and it had no effect. What is causing this? Is there a way to fix it?