Hello @bjrnet21,
The JavaScript combination process is an automated combining of several JavaScript files into a single file, to reduce the total DOM elements when loading a page, as well as reduce the deferring of rendered javascript elements. Because this is an automated process, it relies on the strict standards of writing JavaScript code. If any JavaScript code in your Themes or plugins is written without following the strict code standards, then the automated process may not combine this code properly and result in syntax errors. Since you have an issue with a Premium plugin, we do not have a way to test it. The current case, is most probably not directly related to Yoast. The combination process is most probably breaking into a syntax error due to the merging of all of the front end JavaScript elements of your Theme, your other plugins, plus Yoast, but you see the final result affecting a functionality in Yoast in particular.
In the current case, you or your site developers should check to see in which part of the combined JavaScript file the syntax error occurs. Then find which .js file in your site contains this part of the code and exclude this problematic .js file from the combination process. You can read how to exclude .js file here:
Best regards,
Plamen.M
Tech Support Team
SiteGround.com