H1 too short issue means that h1 tag length on some pages is shorter than 5 characters.
Why it is important
HTML headings are hierarchically organized, with h6 representing the lowest level possible and h1 representing the most important heading. Each heading refers to a specific content area on a page and higher-level headings may engulf multiple lower-level headings together with the content sections the latter accompany.
The h1 heading is equivalent to the title of the page (the headline), while the hierarchical structure of h2-h6 headings can be viewed as forming the outline of the document. The headings are formatted correspondingly to convey their importance – for instance, the h1 heading has typically the largest font size in the entire document.
Typically, a span of 10 characters or less is incredibly little to mention important keywords in an appropriate context. Hence, such a short h1 typically represents wasted opportunity to use an appropriate number of keywords as well as to write an effective heading that would describe the content adequately. It is vital that the h1 is maximally optimized, given the importance of this content area for search engines.
Search Engine Optimization (SEO) Starter Guide made by Google recommends avoiding excessive use of heading tags on a page and very long headings.
How to check the issue
Checking for this issue requires one to access the source code. Do it with the help of this online tool https://codebeautify.org/source-code-viewer. Also, most browsers allow you to view the code. In Chrome, right-click on the page and choose “View page source.”
Once the source code opens, search for text flanked by <h1> which designates h1 tags.
Check your website for short h1 tags
Audit your website to detect pages that have too short h1 tags
How to fix the issue
Edit or rewrite the h1 tag so that it includes all the necessary targeted keywords, while also closely describing the content of the page.