After you install Cumulative Update 14 for Microsoft Exchange Server 2013 and Cumulative Update 3 for Exchange Server 2016, public folder posts may not be indexed if a public folder migration is active. Public folder search results may be missing some items.
For Exchange Server 2013
For Exchange Server 2016
To fix this issue, install Cumulative Update 4 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
Note After you install this update on either version of Exchange Server, you should move the public folder mailbox to a new database to make sure that all items are indexed correctly.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.