Hi,
Sorry for the issues you are having. I can help troubleshoot this with you.
I am not sure why it happened yet, but I believe downgrading to 4.0.5 will resolve the issue.
That is for the Events Calendar found on WordPress.org
This link will download it:
https://downloads.wordpress.org/plugin/the-events-calendar.4.0.5.zip
And you can use this step to manually update:
Manual Updates
This process does not delete events or change settings, but it is a good idea to backup before doing it.
Let me know if that helps get you back on your feet for now.
Thanks