In Exchange Online, you experience one of the following symptoms.
When you create a meeting and then select a conference room list in Scheduling Assistant, the list is displayed briefly but then disappears.
When you create a meeting and then add an individual conference room in Scheduling Assistant, the room is displayed briefly but then disappears.
If you add multiple rooms to a meeting in Scheduling Assistant, the whole list of rooms disappears.
These issues occur if one of the following conditions is true:
Cause 1: The room name contains an ampersand character (&) in the SMTP address.
Cause 2: The room mailbox settings specify invalid working hours. For example, the end-time setting is earlier than the start-time setting.
Cause 3: Incorrect working hours are configured on the mailbox.
Cause 4: The working hours time zone of the user or shared mailbox that’s scheduling the room doesn’t match the working hours time zone of the room.
To resolve the issue that's described in Cause 1, see the following Microsoft Knowledge Base article:
2500176 Room mailbox unexpectedly disappears from an Outlook 2010 meeting invite
To resolve the issue that's described in Cause 2, reset the working hours in the room mailbox to a valid value.
Note You must first locate the affected mailbox or mailboxes. To do this, add the mailboxes from the room list to Scheduling Assistant one at a time until they disappear. The last mailbox that you added is the affected mailbox.
After you locate an affected mailbox, follow these steps:
Grant your account full access permissions to the conference rooms.
Use your account to sign in to Microsoft Outlook Web App.
Click your name in the upper-right corner of the window.
In the Open Other Mailbox box, open the conference room mailbox, click Options, and then click See All Options.
In the navigation pane, click Settings, and then click Calendar.
You may receive an error message. Regardless, change the working hours to something different from their current setting, and then click Save.
To resolve the issue that's described in Cause 3, change the working hours. To do this, follow these steps:
Use the Get-MailboxCalendarConfiguration PowerShell cmdlet to check the WorkingHoursStartTime and WorkingHoursEndTime values.
Use the following PowerShell cmdlets to change the values in PowerShell: Set-MailboxCalendarConfiguration -Identity username -WorkingHoursStartTime hh:mm:ss and Set-MailboxCalendarConfiguration -Identity username -WorkingHoursEndTime hh:mm:ss Note You may receive a "The end time that you entered occurs before the start time. The start time must occur before the end time if the WorkingHoursEndTime is set with a value before WorkingHoursStartTime" warning.
To resolve the issue that's described in Cause 4, change the working hours time zone of the user or shared mailbox to match the room mailbox. To do this, follow these steps:
Use the following PowerShell cmdlet to check the WorkingHoursTimeZone parameter values. Get-MailboxCalendarConfiguration
Use the following PowerShell cmdlet to change the value. Set-MailboxCalendarConfiguration -Identity Mailbox -WorkingHoursTimeZone <ExTimeZoneValue>