If an error is made in a csv file for loading layer as text file QGIS insists on loading the original (faulty) file even though the fault has been corrected and saved. This even persists if QGIS is closed down without saving and then reopened. I cannot understand this perverse behaviour or the reason for it.
Why does QGIS retain and use a CSV file that is incorrect? If the file is corrected QGIS ignores the correction on reload and retains the incorrect version. This persists even if the project is not saved and QGIS shut down. On restart QGIS will still reload incorrect version.
