When applying a Cumulative Update to your SharePoint 2016 Farm, you might run into troubles when executing PSConfig/PSConfigUI after installing the Binaries. The error that is logged in the Windows Event Log looks as follows:

The Execute method of job definition Microsoft.SharePoint.Administration.SPUpgradeJobDefinition (ID ..) threw an exception. More information is included below.

The upgraded database schema doesn’t match the TargetSchema. (Correlation=..)

You can avoid this issue if you either

• dismount all the Content Databases before executing PSConfig/PSConfigUI (which is a good idea in larger environments anyway) and upgrade them later in a second step or
• upgrade all the Content Databases before executing PSConfig/PSConfigUI with something like Get-SPContentDatabase | Upgrade-SPContentDatabase. You could speed up this process by using multiple PowerShell Sessions or even multiple SharePoint Servers.

With detached or already upgraded Content Databases PSConfig/PSConfigUI should run successfully.

Markus