Parallax image won't show on front-end

De background image sometimes won't show up (in theme: Spirit) in the live site (shows white background) when choosing parallax background-type for that region, while the background is shown in the upfront editor. However in both, the "draggable elements" are visible.

When i hard refresh the page, the background image is shown for 2 seconds. Then a "display: none" appears on the div:

<div class="upfront-output-bg-overlay upfront-output-bg-image upfront-output-bg-desktop upfront-parallax" data-bg-parallax=".upfront-bg-image" style="display: none;"><div class="upfront-bg-image upfront-image-lazy upfront-image-lazy-bg upfront-parallax-element upfront-image-lazy-loaded" style="top: -30px; bottom: -30px; background-image: url(http://.....jpg); background-size: 0px 0px; background-position: 0px 0px;" data-src-desktop="//boscotondo.vuora.nl/wp-content/uploads/sites/50/2015/09/slider_centre_court_small.jpg" data-bg-image-ratio-desktop="0.67" data-src="//.....jpg" data-bg-image-ratio="0.67"></div></div>

Maybe it's closely related to, my bug report: https://premium.wpmudev.org/forums/topic/parallax-responsive-mode-bug-report#post-953332