The problem is that if i set resolution for my Ubuntu 18.10 VM (same with 18.04.1) to 1024x768 or 1280x768 some objects only appear on screen when hovering with mouse cursor. 800x600, 1280x800 work fine.
Xubuntu 18.10 works ok with 1024x768, as well as Fedora 29 which also uses Gnome. As i can’t get solution for this in VirtualBox forums, maybe someone here would have a hint.
More detailed information is in VirtualBox forums post: https://forums.virtualbox.org/viewtopic.php?f=3&t=91734