Human Made has a fantastic plugin for automatically offloading WordPress uploads to Amazon S3, but the process involves rewriting the results of wp_upload_dir(), which is used by plugins and themes to determine where the site's uploads/ directory lives. Beaver Builder, meanwhile, writes its cache to disk for improved performance; it's preferred cache directory? uploads/bb-plugin/cache. Starting to see a problem?
This plugin ensures that Beaver Builder is still able to write to the local filesystem, while attachment media is still uploaded to and served from Amazon S3.
Clone or download this repository into your site's plugin directory (wp-content/plugins by default), then activate the plugin via the "Plugins" screen within the WordPress admin panel.
This plugin may also be installed as a "must-use" (MU) plugin — simply copy beaverbuilder-s3.php into wp-content/mu-plugins — no activation necessary!