Good evening Alex and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the 404 error messages you have bumped into.
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/
Secondly, could you try to:
- Re-save your permalinks to see if that helps
- Try temporarily reverting back to a default WordPress theme such as twenty-sixteen to see if that changes anything
Let me know how that goes.
Best regards,
Geoff B.