FYI
Run the script Reset-ScanEngineVersion.ps1 succesfully. Takes apporx. 20 min to download
After running Enable-AntiMalareScanning.ps1 emails stopped inbound. I have not rebooted the Exchange 2019 server and had to disable AntiWalware.
MSExchangeTransport was restarted before and after running any PS scriptsAdmin Exchange shell was used to run the scripts
Extra steps after applying the fix as after enabling AntiMalwareScanning the inbound email started to queue again.
*********** after ResetScanEngineVersion script ************
CD $ExScripts
.\Enable-AntimalwareScanning.ps1
Restart-Service FMS -Force Restart-Service MSExchangeTransport
*********** after ResetScanEngineVersion script ************
This would Stop and Start Microsoft Filtering Management Service & MSExchangeTransport Services or manually Stop / Start FMS Service.
NOTE :
I have noted a slight delay with new inbound emails, even afer the mail queue was empty. Two test emails inbound are missing and never hit the Exchange queue.