Ubuntu VM's screen is often black in VirtualBox

From: Yuri <yuri_at_FreeBSD.org>
Date: Tue, 14 Feb 2023 00:48:40 UTC
I observed this many times: Ubuntu VM comes up with a black screen. 
Sometimes resizing the window helps, and sometimes it doesn't help.


Does anybody know why does this happen, or how to cure this?


Thanks,

Yuri