The order volume in an Opportunity may differ from what you see in Analytics because the two views are measuring slightly different things.
The Opportunity view only includes orders tied to links or content that qualify for that specific Opportunity. For example, a link may need to be created within the Opportunity window and meet the Opportunity’s tracking requirements in order to count.
Analytics may show broader attributed order volume, including activity from links that are associated with the creator or brand but do not qualify for the Opportunity itself.
In short: Analytics shows broader performance, while the Opportunity view only shows performance that meets the Opportunity’s specific tracking rules.