Preview function for supervisors

Our supervisors have access to listen, whisper, and barge into their reports’ calls with no issues, but the button to preview call transcripts appears intermittently. About 75% of the time, the button is greyed out, but for some calls they can click the blue preview button and pop out the live call transcript. I haven’t seen anything about this feature in CC support docs. Has anyone else experienced this, or know if it’s a permission setting on the super or agent end we could fix?