Notify Extra, second batch error

Hi, I'm running Notify extra.
This works great for 25 or less subscribers, but when I get over 25, it starts a second Batch...and it sends 2 emails.

One with the correct email, and another with the placeholder code still there {{+firstname}}.

I get this error.
[2018-11-14 09:23:23] (ERROR @ /paas/c0909/www/core/model/modx/mail/modphpmailer.class.php : 172) You must provide an email address to send to.
[2018-11-14 09:23:23] (ERROR @ /paas/c0909/www/core/components/notify/model/notify/modmailx.class.php : 301) PHP warning: Invalid argument supplied for foreach()

Any idea?

I ended up just increasing the batch size, but I wonder if this is a bug that can be fixed.

[[!Notify@NotifyProperties? &debug=`1` &batchSize=`100`]]

I can't think what would cause this. I use Notify all the time and have never seen this, though I use Mailgun to send all the emails, so there could be a bug in the non-mailgun email class you're using. Unfortunately, I don't have any simple way of testing that, since I'm tied to Mailgun (which gives much better deliverability and great statistics on each send -- hard and soft bounces, opens, etc.). Mailgun is free for up to 10,000 emails per month. It's a little work to set up, but you only have to do it once.