Howdy Rob!,
I would love to help you with this. I had a look at your site and am not seeing that issue with any of the current events. Did this issue already go away, or does it only happen with certain events? If you can point me to an event that it happens on I might be able to identify the source.
If the issue is still happening, it would be worth trying to flush your permalinks. The first heading in this guide will walk you through flushing your permalinks, but visiting the permalinks settings page and hitting save: Troubleshooting 404 Page Not Found error.
I look forward to your response and then I can dive into this further. Cheers!
– Brook