Consider the following scenario in Microsoft Exchange Server 2019 or Exchange Server 2016:
You enable mailbox audit logging.
You create and then delete some number of items in the mailbox that's being audited.
You run Search-MailboxAuditLog -ResultSize where ResultSize is more than the number of events.
As a result, the ResultSize will only be honored if MaxHitsForFullTextIndexSearches has not been modified. If it has been modified, you can increase Outlook search results, and then the ResultSize will be capped at that same number. It's expected that the ResultSize should be honored regardless of the MaxHitsForFullTextIndexSearches setting, or the Outlook search results setting and the Search-MailboxAuditLog -ResultSize should use separate settings.
To fix this issue, install one of the following updates:
Learn about the terminology that Microsoft uses to describe software updates.