H1 duplicates issue means that there are two or more pages on the website that have the same h1 tag.
Why it is important
The hierarchy of headings in an HTML document is as follows: h6 is the lowest level heading, h1 – the highest priority one, while all other headings have intermediary importance – the lower the number, the higher the importance.
Thus, h2 headings could be viewed as the main sections of the article, lower level headings – as hierarchically organized subsections, while the h1 tag – as the title of the article. Headings are styled accordingly so that users visually determine their relative importance – the h1 tag is typically formatted using the biggest font size.
Duplicate h1 headings don’t come with penalties. But identical headings on pages with different content imply that the headings don’t uniquely describe the specific content on each page. You can read more about how Google recognizes duplicate content here.
How to check the issue
Access the source code of the page by following this link https://codebeautify.org/source-code-viewer or by right-clicking a neutral region of the web page in the Chrome browser and picking “View page source” – most other browsers also offer this functionality.
Locate h1 tags by searching for text flanked by <h1>.
How to fix the issue
Edit or rewrite h1 tags so that they specifically match the content of the pages they belong to.
Check your website for duplicate h1 tags
Audit your website to detect whether the site has two and more pages with the same h1 tag