This error is little confusing for me. For populating sitemap we are using SXA. Same settings are working on CM server but not on CD server.
Sitemap.xml show urls but hostname is missing from there. Here is snapshot.
Url => loc should have host name, but it does not show. It should be something like
https://example.com/searchresults but it misses the hostname.
CM are on Azure PaaS App service.