Hi @RRoumieh,
HubSpot’s email tracking is based on invisible one-pixel images. If a recipient has blocked images in their email client (or other privacy protection extensions running in their browser), HubSpot will not recognize the email open.
Links are tracked differently, see here, and doesn’t require images to load. That’s why an email might show as not opened but clicked.
In my experience and according to other users, HubSpot will notice this discrepancy and update the email to show as opened after some time.
Hope this helps!