When using root folder, you need to untrailslash line 178 in b2.php

[jrhager84]

When using root folder with b2, there's an additional trailing slash that breaks the links in the media library.
starting at line 171:

return array( 'ID' => $attachment_id, 'filepath' => $filepath, 'filename' => basename( $filepath ), 'url' => wp_get_attachment_url( $attachment_id ), 'subdir' => trim( $uploads['subdir'], DIRECTORY_SEPARATOR ), 'destpath' => $remote_path . untrailingslashit( $uploads['subdir'] ), 'destfile' => $remote_path . untrailingslashit( $uploads['subdir'] ) . basename( $filepath ), // This is the line that went from trail to untrail 'mime_type' => get_post_mime_type( $attachment_id ) );