Why does Search Console say no referring sitemap when my submitted sitemap is successful?

That message usually isn’t an error. A successful submitted sitemap means Search Console could process the sitemap, while “no referring sitemap” on an individual URL just means Google didn’t associate that particular discovery with a sitemap. It may have found the page through internal links or another crawl path. I’d still check that the sitemap contains the exact canonical URL you want indexed — same protocol, host, and trailing-slash version — and that the page is internally linked. But don’t keep resubmitting the sitemap just to clear that label. Google treats sitemaps as a hint, not a promise that every URL will be crawled or credited to that sitemap.