Youtube - progress bar preview not working

[lip]

Usually you can hover with your mouse over the time/progress bar in any Youtube video and it will show you a preview pic of that time moment.
But that's completely gone since yesterday on any video, regardless if recent or old.

Drives me absolutely mad since it's one of the most important features on Youtube.

Am I the only one?
Any ideas?

[lip]

And today it's back, on every video. Phew. Back to jumping over ads, time filler and idiots.
What was the problem or the solution? No idea. Haven't restarted my PC or even closed the browser (my PC does render work and hence is on 24/7).

But thanks for the eh, help, you all.