Youtube play button invisible

Hi everyone,

Lazy loading embedded videos works perfectly for me. However I am wondering how I can make the red play button visible, because currently it is nowhere to be found.

Initially lazy load did not work, as I have a custom WordPress theme.
After a few hours of puzzling I found out that the theme should include “wp_footer()” in order to activate lazy loading.
Perhaps the Youtub play button overlay should be activated by a different hook, could anyone advice on this?

I am looking forward to your suggestions!