Hi!
Thanks for reaching out to the forums. It seems like you might be facing some conflicts on the permalinks can you make sure to follow this guide for fixing 404 errors. Another thing to look for is any page or site that has the “event/” slug from any post, page or category as this one might conflict with the single events URL structure, also try to change the default slug structure to test if this is non a slug conflict.
Please let me know if you have any other questions about this issue or if there’s anything else I can do for you.
Thanks,
Crisoforo