Check if the email is an Operational email, sent via a batch campaign or Trigger campaign. In Email insights, by default, the email communications only show Batch campaign and not Operational Emails or email sent by Trigger campaign.
To show operational email and emails sent by Trigger campaign,
This will display the data as per your Email Performance Report.
If there are discrepancies even after changing the settings, create a support ticket as a data back-fill may need to be performed.