Hey Patrick,
Sorry to hear about this on your site – the error itself is coming from your theme, and you said things worked fine on another host, so I’m not sure if The Events Calendar is breaking things or if there are other things happening on your site…
To further investigate this, I’d recommend first contacting your web host support and/or your theme developer’s support about this issue.
Next, can you share your system information with us? Here’s how to do that → https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Finally, for now, I’d recommend temporarily deactivating The Events Calendar on your site that does have this error – with The Events Calendar deactivated, does everything work fine? Or do the errors persist even without The Events Calendar active?
Thanks Patrick!