In Microsoft Exchange Server 2019 or Exchange Server 2016, after you respond to an email message with a meeting request in Outlook Online Mode, the appointment doesn't show in any calendar views. You can see the appointment in the List View of your calendar, but the Start and End dates are missing there.
To fix this issue, install one of the following updates:
For Exchange Server 2019, install the Cumulative Update 2 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.
For Exchange Server 2016, install the Cumulative Update 13 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Learn about the terminology that Microsoft uses to describe software updates.