Few pointers which you need to look at.
1 - What is your Exchange CU version? According to my research, similar problems occurred in earlier versions of Exchange. If your Exchange version is lower, please upgrade Exchange to a newer version.
2 - Please run the following command to check whether the Url settings of the EWS virtual directory are correct:
Get-Webservicesvirtualdirectory -showmailboxvirtualdirectories | fl Identity,*url*
3 - Delivery reports for administrators uses the Exchange admin center (EAC) to perform a targeted search of the message tracking logs. So please make sure the message tracking logs usually exist.
4 - Please try to run the following commands to remove and recreate the EWS virtual directory:
Remove-WebServicesVirtualDirectory -Identity <>
New-WebServicesVirtualDirectory -WebSiteName <> -InternalUrl <> -ExternalUrl <>
5 - Please check any related error logs in the event viewer.