A question about "Suppression by Email address or Domain"

I sent out an EDM a couple of days ago to TWO target lists.
I ended up with 108 in “Suppression by Email address or Domain”, but figured out quickly that 104 where found in both target lists - so all good and correct.

I checked a few those 4 email addresses in the target list: not invalid email addresses, not opted out, not marked deleted in the list nor anywhere else.

What could be the reason why the sending of those emails were set to “suppressed”?
Thanks

Hi Jobst, are they possibly duplicated (eg. same email address for a Lead and its converted Contact) ?

Are these email addresses in any suppression Target List you are involving in the Campaign?

They are not in any suppression list - I clean the DB regular so no need for this.

However I found them as converted Leads - we have MANY converted leads and that NEVER has caused any problems.

Ok, good.

Has anyone of them ever unsubscribed from your Campaigns?

Have you possibly send them the same Campaign twice?