When you have a named instance of SQL Server 2016, and you try to install Cumulative Update 1 for SQL Server 2016, the installation fails.
This issue occurs when the named instance is named with a reserved name. For example, if the named instance is named by using any of the following reserved names, this issue occurs:
CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, or LPT9
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.