The issue is that you're relying on the SDK and the plugin JS library for making and generating the button. That means all of LinkedIn's JS libs could be do any number of things to make the button appear and behave as it does. To have a URL-sharing link to Linkedin, all you really ought to need is...
https://www.linkedin.com/sharing/share-offsite/?url={url}
Then you can just make any button, using any HTML, CSS, or JavaScript that you like, and hyperlink it to allow sharing of a page. Like so...
<a href="https://www.linkedin.com/sharing/share-offsite/?url={url}" target="_blank">Share on LinkedIn</a>
Source: Microsoft LinkedIn Share URL Documentation.
If you are interested in a regularly maintained github project that keeps track of this so you don't have to, check it out! Social Share URLs
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