Layer-Slider WP not showing full-width while page is loading

Hi enfold-Team,
recently i changed the background-images of some of our sliders to gradients embedded via CSS to save space. (Layer SLider WP Plugin)
Now I notice that while loading e.g. the frontpage the gradient-background of the slider is not showing full-width from the beginning.
After the page is fully loaded and the animation begins then the slider turns full-width, but before it just spans two-thirds of the space.

This problem probably existed for a longer time but it never showed as we used jpgs as background-images and not coded gradients.
Via DevTools in chrome I was looking at the performance during the loading process but i couldn’t determine which process was exactly causing this problem.
Atm we’re planning to update the Theme to the newest release next week and maybe during that process we can already optimize the page properly afterwards. And i hope that could fix this problem, too.
So maybe it is just an overall performance problem with our website but if you have any hints what could cause this problem i’d be happy to listen to your feedback.