[XFCE] Desktop Blinking

[Danielsan]

Today without any reason my daughter's laptop desktop was blinking, exactly the day she had an important test. I mitigated the issue removing the desktop but it was blinking the same, when I touched the panel or the menu it stopped to blink.

What could be possible happened to the desktop?
The Debian installation on her laptop is pretty vanilla, no fancy franken-debian.

Thanks...