Drupal 8 theme showing Uncaught TypeError: $(…).find(…).once is not a function in console
You're loading 2 versions of jquery: 
assets/js/jquery.min.js: {} 
- core/jquery 

That's most likely your issue. Try removing the assets/js/jquery.min.js entry and flushing your cache. That will mean you're just using Drupal's core jquery which hopefully your plugin should work fine with