I am having this exact same issue. It progressively gets worse and worse and worse (meaning the gap keeps getting bigger and bigger, like the wallpaper is moving down screen) until you have to reboot. If I disable deskscape, the problem goes away when reverting back to the original wallpaper. When I restart it (without having rebooted), the problem continues.
No video is necessary, a simple screenshot illiterates the issue:

The black gap isn't always black, it's usually whatever was on the screen at the time the gap appeared; so it can be a title bar header that you see partially or whatever.
Deskscape Version: 11 BETA 5
Windows 11 Pro: (it has been happening through several windows 11 updates), presently on 21H2 (OS Build 22000.556)
Note, I do not ever shut off my PC; it is on 24/7; it takes days for the problem to occur. Typically, I have a different background running on each monitor (up to 4 monitors).