The download of CentOS 7 was finished and I downloaded Fedora Workstation 27 later. With both as guests the VM still crash, so it's not a issue exclusive to Ubuntu guests.
The crash may happen after 8 resolution changes (CentOS) or in the first one (Fedora 27) or if the system is running and suddenly crashes (Xubuntu 17.10 in a external HDD).
The download of CentOS 7 was finished and I downloaded Fedora Workstation 27 later. With both as guests the VM still crash, so it's not a issue exclusive to Ubuntu guests.
The crash may happen after 8 resolution changes (CentOS) or in the first one (Fedora 27) or if the system is running and suddenly crashes (Xubuntu 17.10 in a external HDD).