If an exception is raised and you set LogExceptions to True, the exception will be logged with a different format, specified by ExceptionFormatString property.
ExceptionFormatString: string
Specifies the format string for the message to be logged when an exception happens during the request processing. In other words, if any exception occurs in the server during request processing, and LogExceptions property is True, the exception will be logged using this format. Different from FormatString property which has a specific format, the content of this property is just a simple string used by Delphi Format function.
Three parameters are passed to the Format function, in this order: The exception message, the exception class name and the log message itself. Default value is: (%1:s) %0:s - %2:s