Hi there,
An issue with a cron would affect the scheduled imports. If you are having issues performing a one time import, then I would say it has nothing to do with a cron.
Can you explain in more detail what happens when it “fails” upon clicking the import button? I was able to successfully import events from the calendar link you provided without any issues. Are there any notifications displayed? If you inspect the page with your browser tools, are there errors in the console?
Also, can you please share your system information with me?
Thanks,
Sky