Hi,
I have a strange situation, a user has filled in the form once and received two emails with a link to download the material. The campaign in his path contains only one email. In the mautic there is a confirmation that only one was sent. What could be the problem?
The same person cannot start the same campaign 2x if you didn’t allow it (allows to restart the campaign)
Yes, I know 
It’s not about restarting the campaign, it’s just that a scenario that involves sending an email sometimes sends 1 and sometimes 2 messages. What’s worse, no matter how many emails he sends, the event history assigned to the contact/person only shows the sending of one message…
Are you saying, that Mautic sends duplicates from the same message?
Are you using the file queue for sending emails?