"T" Missing on Annotation Bar for meeting attendees

Several times now we have had a situation where numerous webinar/meeting attendees cannot see the “T” button selection on their annotation bar. We are unable to discern any kind of pattern (i.e. tablet vs computer, app vs browser, etc...). This most recent one ALL attendees were not able to see the button. The Annotation Bar IS visible. All other tools work, it is only the “T” or text button that is not visible. Does anyone know what this might happen?