Hello @Amy_75 ,
I'd recommend collecting additional evidence from the affected contacts (for example: screenshots of the same, exact email showing up in their inbox multiple times), then calling back into our Deliverability team with that. Deliverability will be far better equipped to look into the issue, and determine if a glitched sendout actually occurred. Those screenshots can help them better determine which contacts were actually affected, and where the issue might have occurred.
Similarly to the Deliverability agent you spoke with today, without some of these contacts explicitly providing screenshots of them receiving the email multiple times, or something to that effect, everything on our end is only showing these emails as being sent once. If a contact was on the Did Not Open List, then that means they didn't open the email - either because they didn't see it / get to it the first time, or because they deleted it outright without looking at it.
The only way a contact could still report as "Did Not Open," and have technically opened the email, is if their email client blocked our tracking from triggering. Even still, the example provided to our Deliverability agent only shows that the contact received both the earlier version and the re-sent version, but only opened the latest one several times, minutes apart - according to their engagement reporting.
If you have several contacts complaining about receiving the new email when they claim to have opened the old one, then you'll want to ask them if their email clients block images and links from populating / showing by default. If that's the case for any of them, implore to them that they need to make sure those are allowed for your emails, otherwise it can negatively affect your ability to communicate with them.