Zoho Calendar dropping attendee names from the list

Zoho Calendar dropping attendee names from the list

Hi,

We are experiencing a problem with Zoho Calendar:  When setting up a meeting if we add external email address as attendees, those people recieve the calendar invitation but their names drop off the Zoho calendar entry - only our internal attendees appear.  This is happening repeatedly and makes it impossible to track who has been invited to a meeting!  Please help