It seems that our friends at Microsoft have done it again and forgotten the importance of testing their updates before releasing them. There are some widespread reports of Outlook instant Search no longer working after installing the December 2018 Security Update KB4471321 for Windows 10 and Server 2016
We have seen this mostly affecting Terminal Server / RDS and Citrix VDA Hosts.
Listed in the known Issues list you will find this mentioned with the following workaround.
To alleviate the symptoms, run sfc /scannow as described in step 3 of Use the System File Checker tool to repair missing or corrupted system files.
It is important to note that the machine will need to be restarted to resolve this completely
- Close all open instances of Outlook
- Open an administrative command prompt by right clicking Command-Prompt and select Run As Administrator
- Type “sfc /scannow” in the command window and press Enter
- .When the scan finishes, restart the computer and test.
Microsoft is working on a resolution and will provide an update in an upcoming release.