Multiple description tags issue means that website has pages with more than one meta description tag.
The importance of the issue
Meta description has a central role in SEO. One could waste incredible amounts of time in optimizing the site and achieving a good page rank, but if the meta description is messed up, it could severely reduce the attractiveness of the web page for users.
This is because meta descriptions are essential in both describing and advertising the content of the web page. Apart from meta titles, these short extracts are the only pieces of information that users obtain from their queries to help them evaluate whether the content of the web page is of any relevance to them. Moreover, the keywords contained in the meta description that will be matching the user query will appear in bold font, signaling to the user that the page is of high relevance.
A page should have only one meta description. If the opposite is true, it is likely the result of an accident, in which case it could create confusion with regard to how the search engine will process the corresponding page and what the SERP snippet would look like.
<…>Google will sometimes use the <meta> description tag from a page to generate a search results snippet if we think it gives users a more accurate description than would be possible purely from the on-page content. A meta description tag should generally inform and interest users with a short, relevant summary of what a particular page is about.<…>
How to check the issue
You should get access to the source code of the page. One way to do this is by using this online tool https://codebeautify.org/source-code-viewer, while another simple way is to right-click on the page in your Chrome browser and choose “View Page Source.” Other browsers should offer similar functionality.
To locate the meta description, just search for <meta name=description.
Checking URLs with multiple description tags is important but not enough to rank good enough!
Check not only the issue but make a full audit to find out and fix your technical SEO.
How to fix this issue
Remove extra description tags. Leave just one.
As part of some advanced techniques, it is possible to embed several meta descriptions in a single page so that search engines can “choose” the appropriate one when creating the SERP snippet. Suppose you have three different targeted keywords on the same page and you write corresponding meta descriptions for each of these keywords.
The purpose is to make the search engine display meta description 1 when the user queries match keyword 1, to display meta description 2 when keyword 2 is matched, and so on. Nevertheless, this is not guaranteed to work and each search engine might treat the code differently, hence, these methods should be used with great caution.
Detect multiple description tags
Crawl the website to collect all pages with more than one meta description tag