I am running Virtualbox Version 5.2.8 r121009 (Qt5.6.2) on a Windows 10 Enterprise host. Whenever I start Teamviewer on the host my (already started) guests all crash. They become unresponsive and do not respond to anything any more. The OS of the guests does not matter, all guests just stop functioning. The only thing I can do is close them with the Windows close button. Normally this button will show me a popup giving me options about shutting down the guest, but these don't show. The VB Manager window then shows the VM with the status "Stopped". When starting the guest again it starts like the guest OS has been turned off unexpectedly.
The fix for this is to turn off the Quickconnect button from teamviewer. This button will be drawn on all running Windows applications. I didn't use that button anyway but the fact that it crashes VB guests is not a good thing.