The plugin works by overriding the file path of attachments that don’t exist on disk with their URL.
Signs you need the plugin:
The debug dump complains of files not existing
The attachment files do not exist on disk
The attachments are reachable if you visit their URL
Enabling the plugin will, when it is time to broadcast, check if the attachment that is about to be copied exists on disk. If the file can not be found, the file path is replaced with the URL and Broadcast can then assume that the file exists on a CDN.
Users report the following CDNs require this workaround: