s.Emailaddress as 'Email_Address'
FROM _Subscribers s
JOIN _Sent se ON s.Subscriberkey = se.Subscriberkey
- is anything wrong with it? or is this a support/account issue?
You need to run this in the ENT BU to get records, as it sounds that you might have a subscriber filter configured.
When you send an email to a data extension, the contacts will always be added to All Subscribers in ENT BU. These are shared across the enterprise, however you can manage subscribers so they only appear at a specific child business unit level. This is done using 'Business Unit Subscriber Filters'.
Go to Administration > Business Units Select the child business unit, and click "Define Subscriber Filter"
When you configure a filter on the business unit, only the subscribers who match the rule will appear in All Subscribers of the child business unit. The parent Business Unit will always have the complete list, though.