Good evening Cynthia and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the 404 URLs you have been getting.
I would love to help you with this topic.
First off, to be completely transparent, normally the word “permalink” should not be part of any URL. The %5B and %5D from the URL you shared are html for brackets (which are not supported in a URL, hence the 404)
Out of curiosity, would you mind sharing a screenshot of what the permalink settings for your site are (in a private reply) ?
Could you also please go through our testing for conflicts procedure (preferably in a staging/dev environment or local install of your WordPress website) and let us know what you find out ?
Basically the goal here is to revert back to a bare WordPress installation to see if the problem persists. It also allows us to pinpoint what the cause of the issue is.
I know this might be time consuming, but it is truly the fastest way to come to a resolution.
Let me know how that goes.
Best regards,
Geoff B.