The sync of the "was delivered email" seems to be lagging. Since a while back it is working only on some (seemingly random) persons within each email blast, and failing to sync the info on others. It doesn't seem to correlate with whether it's a lead or a contact in SFDC. Some of them show "email was opened" in SFDC but still not "sent" or "delivered". Some show only "sent" or "sent" And "opened". In short, "opened" seems to work fine but the others are lagging.
I would appreciate some clarity on this!
Only one Delivered (or any enabled synced activity) event will sync per person, per day. So if someone is delivered two emails in the same day, only the first one will sync. Do they lead/contact you're checking have more than one delivered email in the same day?