If you have image URLs in your CSV file, these images are downloaded locally and then WordPress generates different image sizes which are specified in your WordPress Media settings. This process may take long time. You may see a white screen depending on the number of records to be imported or if you have multiple images per record.
In this case, do not navigate away from the screen, open up a browser tab screen and go to Media Library and see more images are getting created. If no more images are getting created, refresh the white screen, count the number of records imported. If the record number matches the number of records in your CSV file, check if the records were imported correctly. If not, repeat the same process but this time, check the update button in the import mapping screen.