Why it matters
That's correct for duplicates and syndicated copies, but a template bug (every page canonicalising to the home page, or to page 1 of a series) de-indexes the site.
How to fix it
Verify it's intentional. Content pages, paginated pages and locale variants should each be self-canonical.
References
More seo rules
void seo reports 60 rules in this category. What search engines need from the raw response: status codes, titles and descriptions in <head>, self-referencing canonicals, one h1, crawlable links, Open Graph, icons, robots.txt and a sitemap with real dates.
canonical-missingNo single rel=canonical in <head>canonical-invalidCanonical URL is relative or contains a fragmentcanonical-brokenCanonical points to a URL that returns 4xx/5xxcanonical-conflictCanonical target redirects, is noindex, or canonicalises elsewherehead-js-mutationJavaScript changes canonical, robots, title or description after loadh1-countPage doesn't have exactly one visible <h1> in the server HTMLh1-title-mismatch<h1> and <title> share little wordingheading-skipHeading levels skip (h2 → h4) or headings are empty