Symptoms
If an Offline Address Book (OAB) Generation Request is sent before the completion of OAB generation, and if the OabProcessingThreshold value is exceeded (the default value is 0 minutes for Exchange On-Premises), the OAB generation process restarts. After you install Microsoft Exchange Server Cumulative Update 13 (CU13), the default value is changed to six hours.
Resolution
To fix this issue, install Cumulative Update 13 or a later cumulative update for Exchange Server 2019.
