A new user would need to do a support ticket to turn on the Google Sheet export option, as described here: How do I export a large project with custom fields and subtasks into a CSV or spreadsheet - #12 by Mihow
It’s possible that something has happened that means you need to file a ticket again, even though you’ve had this in the past. I would try that.
(NOTE: I am a user and customer of Asana, not employed by them. I help people here voluntarily. 
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