Symptoms
Transport rules that use attachment metadata to trigger actions will trigger only when the first item that's attached contains the metadata in Microsoft Exchange Server 2019 or Exchange Server 2016.
Resolution
To fix this issue, install one of the following updates:
For Exchange Server 2019, install the Cumulative Update 6 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.
For Exchange Server 2016, install the Cumulative Update 17 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
References
Learn about the terminology that Microsoft uses to describe software updates.