Hi Hyla!
I’m sorry you are having that issue. Let me help you troubleshooting that.
Could you please share the CSV file with us so we can make some tests on our end?
CSV imports are all managed by The Events Calendar, so if you want to try downgrading you should already be able to get a previous version of it from your Downloads page.
For the moment I’d recommend you stick to the latest version of our plugin, which is 4.5.10.1 because it might include fixes and improvements related to your issue.
I can see you are currently using version 4.5.10. Please update to the latest version and see if that solves the problem.
Thanks,
Victor