OpenGL ping pong feedback texture not completely clearing itself. Trail is left behind

The goal:

Effectively read and write to the same texture, like how Shadertoy does their buffers.

The setup:

I have a basic feedback system with 2 textures each connected to a framebuffer. As I render to frame buffer 1, I bind Texture 2 for sampling in the shader. Then, as I render to frame buffer 2, I bind texture 1 for sampling, and repeat. Finally, I output texture 1 to the whole screen with the default frame buffer and a sperate shader.

The issue:

This almost works as intended as I'm able to read from the texture in the shader and also output to it, creating the desired feedback loop.

The problem is that the frame buffers do not clear completely to black it seems.

To test, I made a simple trailing effect.

In shadertoy, the trail completely disappears as intended:

Live in shadertoy

But in my app, the trail begins to disappear, but leaves a small amount behind:

My thoughts are I'm not clearing the frame buffers correctly or I am not using GLFW's double buffering correctly in this instance. I've tried every combination of clearing the framebuffers but I must be missing something here.

The code:

Here is the trailing effect shader with a moving circle (Same as above images)

#version 330
precision highp float;

uniform sampler2D samplerA; // Texture sampler

uniform float uTime; // current execution time
uniform vec2 uResolution; // resolution of window

void main()
{
    vec2 uv = gl_FragCoord.xy / uResolution.xy; // Coordinates from 0 - 1
    vec3 tex = texture(samplerA, uv).xyz;// Read ping pong texture that we are writing to 

    vec2 pos = .3*vec2(cos(uTime), sin(uTime)); // Circle position (circular motion around screen)
    vec3 c = mix(vec3(1.), vec3(0), step(.0, length(uv - pos)-.07)); // Circle color

    tex = mix(c, tex, .981); // Replace some circle color with the texture color

    gl_FragColor = vec4(tex, 1.0); // Output to texture
}

Frame buffer and texture creation:

// -- Generate frame buffer 1 --
glGenFramebuffers(1, &frameBuffer1);
glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer1);


// Generate texture 1
glGenTextures(1, &texture1);

// Bind the newly created texture
glBindTexture(GL_TEXTURE_2D, texture1);

// Create an empty image
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1920, 1080, 0, GL_RGBA, GL_FLOAT, 0);

// Nearest filtering, for sampling
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

// Attach output texture to frame buffer
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture1, 0);



// -- Generate frame buffer 2 --
glGenFramebuffers(1, &frameBuffer2);
glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer2);


// Generate texture 2
glGenTextures(1, &texture2);

// Bind the newly created texture
glBindTexture(GL_TEXTURE_2D, texture2);

// Create an empty image
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1920, 1080, 0, GL_RGBA, GL_FLOAT, 0);

// Nearest filtering, for sampling
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

// Attach texture 2 to frame buffer 2
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture2, 0);

Main loop:

while(programIsRunning){

// Draw scene twice, once to frame buffer 1 and once to frame buffer 2 
for (int i = 0; i < 2; i++)
{
    // Start trailing effect shader program
    glUseProgram(program);

    glViewport(0, 0, platform.windowWidth(), platform.windowHeight());


    // Write to frame buffer 1
    if (i == 0)
    {
        // Bind and clear frame buffer 1
        glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer1); 
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Bind texture 2 for sampler
        glActiveTexture(GL_TEXTURE0 + 0);
        glBindTexture(GL_TEXTURE_2D, texture2); 
        glUniform1i(uniforms.samplerA, 0);
    }
    else // Write to frame buffer 2
    {
        // Bind and clear frame buffer 2
        glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer2);
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Bind texture 1 for sampler
        glActiveTexture(GL_TEXTURE0 + 0);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glUniform1i(uniforms.samplerA, 0);
    }

    // Render to screen
    glDrawArrays(GL_TRIANGLES, 0, 6);
}


// Start screen shader program
glUseProgram(screenProgram);

// Bind default frame buffer
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);

glViewport(0, 0, platform.windowWidth(), platform.windowHeight());


// Bind texture 1 for sampler (binding texture 2 should be the same?)
glActiveTexture(GL_TEXTURE0 + 0);
glBindTexture(GL_TEXTURE_2D, texture1);
glUniform1i(uniforms.samplerA, 0);



// Draw final rectangle to screen
glDrawArrays(GL_TRIANGLES, 0, 6);

// Swap glfw buffers
glfwSwapBuffers(platform.window());

}

If this is an issue with clearing I would really like to know why. Changing which frame buffer gets cleared doesn't seem to change anything. I will keep experimenting in the meantime. Thank you!