After applying September 2018 .NET 4.6 or later updates, SharePoint crawl can fail and you will see ULS log entries with event ID fa45 or 88bl similar to the following:
mssdmn.exe (0x2730) 0x00D8 SharePoint Foundation Database fa45 High System.TypeInitializationException: The type initializer for 'System.Data.SqlClient.SqlConnection' threw an exception. ...
To resolve this issue you need to ensure that the SqlColumnEncryptionEnclaveProviders configuration section is defined in the config file of the affected application (for SharePoint crawl it would be the mssdmn.exe.config file) or the machine.config to address the issue for all applications on the affected machine.
The mssdmn.exe.config would look like this after the update:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<configSections>
<section name="SqlColumnEncryptionEnclaveProviders"
type="System.Data.SqlClient.SqlColumnEncryptionEnclaveProviderConfigurationSection, System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
</configSections>
</configuration>
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You can find the mssdmn.exe.config in the following locations:
- for SharePoint 2013: C:\Program Files\Microsoft Office Servers\15.0\bin\mssdmn.exe.config
- for SharePoint Server 2016 and 2019: C:\Program Files\Microsoft Office Servers\16.0\bin\mssdmn.exe.config
More details of the issue and a script to update the machine.config file can be found in the following article: