For an unchanged discovered URL set on the same plan, OptinStack selects pages deterministically. The observed Tracker total can still vary because tags load conditionally, third-party requests time out, experiments change, or the site's tag-manager configuration changes between runs.
Compare the scanned URL set as well as the inventory. A changed sitemap, homepage links, hostname, or plan can change the selected pages. If one Tracker is business-critical, add it manually rather than relying only on a future scan observing it.
Documentation: Domain Scan consistency and Why Tracker counts differ.