Hey Michael,
Thanks for reaching out!
Sorry to hear about this issue.
I would need your help in trying to find what causes this.
Could you please go through our conflict testing guide and see which plugin might be causing this?
On what pages are you getting this error? All the calendar pages or only some?
The Query Monitor plugin can also help uncover some more details. Please share with me the full query / queries which are causing this issue.
This all can help track down the source of the issue.
Thanks!
Andras