Amazon-web-services – Amazon S3 bucket returning 403 Forbidden

I've recently inherited a Rails app that uses S3 for storage of assets. I have transferred all assets to my S3 bucket with no issues. However, when I alter the app to point to the new bucket I get 403 Forbidden Status.

My S3 bucket is set up with the following settings:

Permissions

Everyone can list

Bucket Policy

{
 "Version": "2012-10-17",
 "Statement": [
    {
        "Sid": "PublicReadGetObject",
        "Effect": "Allow",
        "Principal": "*",
        "Action": "s3:GetObject",
        "Resource": "arn:aws:s3:::bucketname/*"
    }
 ]
}

CORS Configuration

<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
    <CORSRule>
        <AllowedOrigin>*</AllowedOrigin>
        <AllowedMethod>GET</AllowedMethod>
        <MaxAgeSeconds>3000</MaxAgeSeconds>
    </CORSRule>
    <CORSRule>
        <AllowedOrigin>https://www.appdomain.com</AllowedOrigin>
        <AllowedMethod>PUT</AllowedMethod>
        <AllowedMethod>POST</AllowedMethod>
        <AllowedMethod>DELETE</AllowedMethod>
        <AllowedHeader>*</AllowedHeader>
    </CORSRule>
</CORSConfiguration>

Static Web Hosting

Enabled.

What else can I do to allow the public to reach these assets?