Good evening Rob and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the widget not working on your site.
I would love to help you with this topic.
As a first troubleshooting step, could you please provide us with your complete system information in a private reply using the instructions found in the following link?
https://theeventscalendar.com/knowledgebase/sharing-sys-info/
I took a look at your website and I am seeing an error message for JQMigrate (through the Google Chrome Developer Tools).
That Javascript error is most likely breaking the proper functioning of the calendar widget.
Could you also please go through our testing for conflicts procedure (preferably in a staging/dev environment or local install of your WordPress website) and let us know what you find out.
Basically the goal here is to revert back to a bare WordPress installation to see if the problem persists. It also allows us to pinpoint what the cause of the issue is.
Let me know how that goes.
Best regards,
Geoff B.