Comment 5 for bug 1605836

I too am having the Unity not starting problem.
It was working this morning but then I applied the latest updates and now it's broken.
I'm using Ubuntu Desktop 16.04 on VirtualBox 5.1.2 on Windows 10 Pro 64 bit.
I've tried:
- downgrading VirtualBox to version 5.0.26
- changing the VMs chipset to ICH9 (was PIIX3)
- changing the VM to having 1 vCPU (was 4)
- booting the 4.4.0-28 kernel instead of the default 4.4.0-31
- enabling PAE/NX
- changing networking to not use virtio-net
- changing paravirtualisation acceleration from Default (KVM) to none

None of the above has made any difference (so I've undone all those changes).
My VM is a default setup VirtualBox Ubuntu VM with 4 GB RAM, 4 vCPUs, USB 3.0 enabled, virtio-net.

Recent Ubuntu updates seem to be the culprit. I noticed that since a couple of days ago, every fifth boot will result in an NMI watchdog timeout with CPU stuck for 23s.

Is this a DBUS issue?