When you upload a .CSV file and select Key to Bulk Update and select the fields in Tables for importing to update, you can not import in to the fields located in Tables. The import function does not work for updating and adding data in Tables.
What is Key to Bulk Update? Key to Bulk Update is used to update existing records in apps with data from a .CSV or Excel file. Data from the spreadsheet is compared to a Key Identifier field. If this field matches a record that already exists in the app, the data is updated. If there is no existing record in the app that matches the file, a new record is added.
What is a Table? For more information on tables in kintone see How to Create a Table, or see the image below of an example Table.
To successfully import and update your records, delete the Table field columns from the file and import only those fields that are not located within a Table, or do not select the fields in Tables to import in the settings.