Hi,
I tried to replicate this a few times with the sample CSV file, but I didn’t get an error. Are you able to import the sample without errors?
Two other things to try:
1. There are some plugins that will display the WP logs, even if you don’t have FTP access, so it might be worth checking those out.
2. Deactivate ALL other plugins and switch to a standard theme (like twenty twenty-five). If the import works, you can reactivate one by one to find the error.
If you can share an administrator login to a staging site where I can see the problem then I can debug it there.
If you’d like to send the file, you can reach me with the contact form and I’ll reply. But from what you describe it sounds like the issue may be specific to your site.