Consider the following scenario:
You create a mailbox in Microsoft Exchange Server 2019 or Microsoft Exchange Server 2016.
You log on to the new mailbox in Microsoft Outlook.
You copy a message to any folder.
You log off of Outlook.
You log on to Outlook on the web, and open the same message.
In this scenario, the message body is blank in Outlook on the web even though you can still see the content in Outlook.
To fix this issue, install the following cumulative update, as appropriate:
Learn about the terminology that Microsoft uses to describe software updates.