Volume and Brightness slider gone

I use volume up/down buttons and brightness buttons on my laptop when it’s necessary rather than using my touchpad but it’s been a few days that the sliders that show up when you click volume up or down or brightness up or down is not showing up. Yes, they work but there’s no slider available. What could be the reason of the sudden disappearance and how can I bring them back?

I believe they have entries in the notification settings.