This is not firmly reproducible but when I run ctrl+wv to create a vertical split window, I sometimes lose visibility to the colon command prompt. Command prompt still works invisibly. Sometimes I can see the thin red bar of the top of an error message at the very bottom of the window, but there is no way to scroll it into view. Some commands will restore its visibility, :so=2 and also if I select Help/Version from the gnome command bar.
I am getting used to this but it is slowing me down...
I am running gvim 8.0.1453 on ubuntu 18.04.1 LTS gnome 3.28.2.
I noticed this related question but it relates to horizontal splits. It is similar in that window split commands seem unreliable with respect to command line visibility while fullscreen gvim.