Hello there,
Thank you for contacting us.
In the lite version, by default emails are sent using WordPress cron. WordPress requires regular site traffic to run scheduled jobs on time.
In case there isn’t sufficient traffic to run the scheduled jobs, then it might be possible that emails won’t be sent in a timely manner. We suspect the issue might not be due to conflict with WP Cerber as we have checked it at our end and couldn’t find any issue when the WP Cerber plugin is running.
Hence can you please confirm if WordPress cron is running smoothly on your site? To confirm it, you can go to the dashboard menu Tools –> Site Health and check if there aren’t any warning related to scheduled events being delayed or failed?
Hope this helps you. Let us know what comes out in your debugging.
Thank you.