Custom 404 page working for entire site

We have a custom 404 page ( that works.

But when users are browsing our dynamic pages, they don’t land on the custom 404 page, but the old wix one.

This is a working dynamic page:

And here is one that does not work.

How can we make sure our custom 404 page works for the entire site?


This question has been asked before, and as far as I remember no one here had an answer.
Maybe Wix Support will be able to help.