Nino_Bilic thanks for the reply and suggestions re the search issue. Further reading led me to https://support.microsoft.com/en-us/topic/incomplete-search-results-after-installing-an-exchange-server-2019-update-96ae2ef0-4569-4327-8d0c-8a3c1abdc1f6
which gave me hope as it is supposed to reset the search service to begin indexing all our missed emails over the last 12 months. Sadly this has not helped. After leaving the server with the override enabled for 6 days, the index count remains the same and performance of our DAG was terrible with Outlook Clients regularly "not responding" on local devices. I have now disabled the override.
Should I open another ticket with MS, or is there still work to be done on the Bugfunnel issues with Exchange 2019?
thanks