H1 = Title issue means that h1 tag and title tag on the page are the same.
The importance of the issue
The h1 tag is the HTML heading with the highest level of importance. By contrast, h2 headings have lower importance and designate the main sections of the article. Each h2 heading might contain multiple h3 subheadings and the latter might contain lower-level headings like h4, h5, and h6 (which is the lowest level possible).
Putting together all h6-h2 headings by respecting their hierarchy, one would obtain an outline of the document, while the h1 tag would be equivalent to the headline or title of the article. The h1 tag would also be typically formatted with the largest font size on the page, given that headings are normally styled according to their importance.
Although they have a fairly similar goal, the h1 tag and the meta title are displayed differently. Despite the fact that there is no penalty for them being identical, the h1 presents a valuable opportunity to include additional keywords that didn’t fit into the meta title. You can read more about how Google recognizes duplicate content here.
How to check the issue
Check the source code. Access the page with your Chrome browser, right-click it, and pick “View page source” (this method differs in other browsers). This simple online tool https://codebeautify.org/source-code-viewer will also help you access the source code.
To locate the h1 tag and meta title, look for <h1> and <title>, respectively and compare these two.
Detect pages where title = h1
Crawl the website to collect all pages where h1 and title tags are the same
How to fix this issue
Consider rewriting the h1 tag by including overlooked keywords and making it highly relevant for the page.