Content of all sections shows briefly upon load or refresh

Hi

I have videos (mp4 playing via jwplayer) in the various collapsed sections on my site:
https://danaobleman.com/webinar-videos/

When I load or reload the page, the video start screens are briefly visible. This is happening in FF and Chrome.

Has anyone else seen this?

Thanks

https://www.ads-software.com/plugins/jquery-collapse-o-matic/