Strange Campaign Behaviours

For some strange reason of late one of my clients instances started acting really strange.

I launch a campaign and then I see that only part of the emails have been sent.

First mailer in campaign shows the following:

Second mailer in the campaign shows:

Inside the campaign it seems that everything is running okay

I have no idea how to even begin to debug this.

Any ideas ?

Hello Mike!

An email sending campaign action is considered successful when an email is queued OR sent OR scheduled. If you swap the email sent during the campaign, the action keeps counting the successful sends, queues, scheduled emails.

For example:

You have a nurturing campaign that consists of 3 email.
Mautic will send email 1, schedule email 2 both have sucess as action.