I've recently upgraded from Ubuntu Server 14.04 to 16.04.1 and I am experiencing this issue right now.
I tried to purge and reinstall nfs-kernel-server, but the issue came back at once. I was only able to work around this issue by adding
systemctl restart nfs-kernel-server
in /etc/rc.local.
So, from my perspective the issue might be gone for a clean install of Ubuntu 16.04.1, but not for systems having been upgraded from an older release.
I've recently upgraded from Ubuntu Server 14.04 to 16.04.1 and I am experiencing this issue right now.
I tried to purge and reinstall nfs-kernel-server, but the issue came back at once. I was only able to work around this issue by adding
systemctl restart nfs-kernel-server
in /etc/rc.local.
So, from my perspective the issue might be gone for a clean install of Ubuntu 16.04.1, but not for systems having been upgraded from an older release.