I am running Ubuntu 17.10 on VirtualBox 5.2.8 r121009 (Qt5.6.3) on a Mac Pro with MacOS 10.13.3.
On some applications Ubuntu flashes to a grey background at a rate of once or twice a second. On Firefox this lasts for perhaps ten seconds and then runs OK, on Terminal a couple of flashes when it starts and on RPCemu (a RISC OS emulator) it flashes hard and continually and I can do nothing with that application and have to 'Power Off' within VirtualBox.
I have completely recreated the VirtualBox environment several times and changed Ubuntu from 16.04 (where I could not load the core application facilities I needed) to 17.10. Apart from the flashing screen Ubuntu 17.10 is working well.
On some applications Ubuntu flashes to a grey background at a rate of once or twice a second. On Firefox this lasts for perhaps ten seconds and then runs OK, on Terminal a couple of flashes when it starts and on RPCemu (a RISC OS emulator) it flashes hard and continually and I can do nothing with that application and have to 'Power Off' within VirtualBox.
I have completely recreated the VirtualBox environment several times and changed Ubuntu from 16.04 (where I could not load the core application facilities I needed) to 17.10. Apart from the flashing screen Ubuntu 17.10 is working well.