The dashes or hyphens (--) displayed in place of Maintain/Revoke action buttons is an expected behaviour as we intentionally do not show buttons for members or entitlements of the role
that were not part of the role when the review was generated/refreshed.  That is, the reviews are done on the snapshot of the data taken for the certain period and not on the actual data.

Hence, a member collected after Review generation or last Review refresh are not considered in the review, but there is option if you want to include them and that can be achieved by Review Refresh.