Layerslider button randomly disappears

Hello dear developers,
I’ve inquired about this before and tried to fix myself, but I just cant do it so I have to post again. Ill try to explain as clear as possible. There is a layerslider on my landing page and it has an Icon layer that acts as a play-button for a youtube video. I open it in a lightbox using rel=prettyPhoto. This layer is only on the first slide. This button doesnt work correctly. The problem now is that it sometimes appears and sometimes it doesnt. Its wierd to replicate the error. Earlier today everything was fine – the button was there on the first layer of the slider as intended. But now I can refresh (hit f5) on my landing page as many times as I want – the button just wont show. I havent made any changes to the slider today.
Ive tried a few things to fix. Right now i added two icosn with identical function on top of each other – both dont show anymore.
I dont know what to do anymore. Seems like a caching problem? maybe a caching plugin will fix? Help is greatly appreciated.