OJS 3.1.2 sitemap mishandling custom page URL

We upgraded to OJS 3.1.2 last month and today I received a notification from Google’s webmaster tools site indicating that Google was getting a 404 error at one of the URLs submitted in our journal’s auto-generated sitemap.

The problem turns out to be a custom, static page that served as an image gallery to accompany a past issue. (I don’t know if this is related to the problem, but when we were using OJS 2.x we set the image gallery page up as a static page and after the upgrade to 3.1.2 the page was activated as a custom page under navigation menu items.)

The page’s URL is our journal’s base URL + “/pages/view/2018gallery” but is listed in our autogenerated sitemap xml file with %-encoding, i.e. “pages%2Fview%2F2018gallery” . Sure enough, the %-encoded address returns a 404 error. Is there a way to retain the URL for our image gallery without the sitemap reporting an incorrect URL?