Sort the search results on the member search by a custom field

I am returning the sorted Users list from my widget extension, but the users are no longer being filtered on the Member Search page. How can I get the filtering working again?

There is not enough information here to answer this because we don't know what you did or how anything was implemented.  If the expectation is that you added your own extension to replace a call on that page and it would just work, then that won't be the case.