Looks like there may be an issue with the plugin. We’ll get back to you when we’ve pinpointed the problem.
Can you provide a link to your site so we can take a look?
We’ve tracked this down to a bug in the way WordPress core is processing wp_mail (https://core.trac.wordpress.org/ticket/39360). It appears to have been closed and opened under different circumstances and the Core team has recently tagged this bug to be released in WP 4.8
In the mean time we’ve included a permanent fix in the latest minor update to our plugin (https://downloads.wordpress.org/plugin/ldd-directory-lite.zip)
