u/EXkurogane

I've noticed that if I search for a certain topic on YouTube, some of the videos in search results do not have their thumbnail displayed, instead it's a random frame from the video itself, as if a thumbnail was not uploaded. It applies to both my videos and also other YouTubers' videos. And if I refresh the results enough sometimes the thumbnail does come back. That's the situation on both the android app and on desktop.

Is this a known problem on YouTube and how long has this been going on? Thumbnails are such an important aspect of videos to get people to watch them.