WP Rocket
If you are using WP Rocket, you might experience issues with its minification which changes the loading order of our files.
WP Rocket has an exclude option, where you should write this to the exclude css option:
/wp-content/cache/nextend/(.*).css /wp-content/plugins/nextend-smart-slider3-pro/(.*).css /wp-content/plugins/smart-slider-3/(.*).css
and this to the exclude js:
/wp-content/cache/nextend/(.*).js /wp-content/plugins/nextend-smart-slider3-pro/(.*).js /wp-content/plugins/smart-slider-3/(.*).js
These are the places from where we are calling in our files, so this should make the minification to skip them.
If the problem still persists, go to the Framework Settings and under the JavaScript part turn on the Async option, also under the CSS part turn on the Async option.