Data is lost when modifying and then saving a .csv. This occurs in 7.5.8.2 and 7.6.4.1 but not in 7.3.1.3.
From https://ask.libreoffice.org/t/bug-202312-calc-data-lost-during-saving-csv/99947

Steps to recreate:
1. Create new spreadsheet and enter 0 in A1 & A2, a in B1 & B2
2. Save as Text CSV (*.csv), filters:
   * Unicode (UTF-8)
   * Filter delimiter ;
   * String delimiter "
   * Save cell content as shown
   * Quote all text cells
3. In another spreadsheet in each of cells A:A3 enter b Copy the three cells then paste as unformatted text into B1 in test spreadsheet
4. Select cells A1:A3 and press Ctrl+D to fill down
5. Click Save. 
6. Click *File > Reload*. Only 2 rows of data are available, not three

Expected result, all 6 cells are saved