The picker pre-calculates the audience size only for groups that need no extra input. Groups that depend on a value you have not entered yet – ... on X day (needs Trigger Date), People with Digital Balance <=> X (needs Trigger Compare Value) and People who made more than X checkouts (needs Trigger Checkouts Count) – show no count in the modal. After you select them and fill the field, the Review step's recipient summary and View Recipients show the real number. Counts are also omitted when a segment cannot be evaluated in advance for your account (for example when a related module has no data).