How exactly are you sending these emails? The email connection alone is not enough, it is just one of many requirements. You would have to either use one of the sales extensions or use the BCC address:
If you share more details about how you are sending emails, I can elaborate.
That would be the explanation then, please see my previous reply. You would have to use the extensions, the BCC address or send directly from the HubSpot CRM for emails to log.