Per LinkedIn, when a link is shared that's greater than 26 characters, LinkedIn automatically shortens it once you click Post. It will shorten to a lnkd.in domain. You will want to keep your URLs to less than 26 characters for LinkedIn posts. For more information, see LinkedIn's Help Center article.
If you have a shortened link that is reverting to lnkd.in and is less than 26 characters, please reach out to our support team at bitly.is/supportive.