In CSVReader controller service, the value of the CSV Format property can either be 'Custom Format' or some built-in format with predefined parameters (RFC 4180, Microsoft Excel, etc.). When 'Custom Format' is selected, the user-defined (or default) values of other properties, like 'Value Separator', 'Record Separator', 'Escape Character', etc. are used. However, when one of the built-in formats is used, the user-defined (or default) values of these properties are ignored and the format-specific settings are used (e.g. with RFC 4180, the delimiter is the comma, and the escape character is not set) yet, the user can still manipulate the values of these properties of the controller service but they will be ignored which might lead to confusion. It would make sense to hide the properties that cannot be overridden when a built-in format is selected.
Also, the settings of the built-in formats do not appear in the NiFi documentation. The built-in formats come from a 3rd party library org.apache.commons.csv.CSVFormat (in case of the Apache Commons parser). It would be useful to add the link to the CSVReader documentation that points to these settings.