Desktop Preview appears below, not on top of other windows.

[El Servas]

I have positioned my Desktop Preview window on the bottom right corner of my screen. I constantly show it/hide it.

Lately, the DP window has beginning to appear BELOW the taskbar, and if I have other windows (like a maximized Chrome) on that same area, the DP will appear below as well.
It's very annoying and sometimes if I just switch desktops (using the keyboard) the problem goes away. Maybe after a while, it will happen again.
Is it there something we can diagnose?

Thank you.