network-manager can't connect and edit VPN connections. VPN tab disappeared in edit dialog.

[luckyrings]

The VPN tab disappeared while editing VPN connections (e.g. vpnc). Also existing connections can't conncect any more. They ask while connecting for username and password and then fail.

Even new set up VPN connections shows after saving same behaviour.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: network-manager 1.2.6-0ubuntu0.16.04.1
Uname: Linux 4.11.1-041101-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
Date: Thu May 18 15:24:11 2017
EcryptfsInUse: Yes
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
InstallationDate: Installed on 2016-10-28 (201 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
IpRoute:
 default via 192.168.1.1 dev wlp3s0 proto static metric 600
 169.254.0.0/16 dev wlp3s0 scope link metric 1000
 192.168.1.0/24 dev wlp3s0 proto kernel scope link src 192.168.1.23 metric 600
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH CONNECTION CON-UUID CON-PATH
 wlp3s0 wifi connected /org/freedesktop/NetworkManager/Devices/0 home 4545d823-5809-4765-b37b-d94ef11a9956 /org/freedesktop/NetworkManager/ActiveConnection/0
 enp0s25 ethernet unavailable /org/freedesktop/NetworkManager/Devices/1 -- -- --
 cdc-wdm2 gsm unavailable /org/freedesktop/NetworkManager/Devices/3 -- -- --
 lo loopback unmanaged /org/freedesktop/NetworkManager/Devices/2 -- -- --
nmcli-nm:
 RUNNING VERSION STATE STARTUP CONNECTIVITY NETWORKING WIFI-HW WIFI WWAN-HW WWAN
 running 1.2.6 connected started full enabled enabled enabled enabled enabled

[luckyrings (d8f2)]

this is how the edit windows form a vpn connection named "PureVPN" looks like

the text input field "connection name" is greyed out, can't be edited and the register/tab named VPN is missing at all.

[luckyrings (d8f2)]

kernel 4.11.1 is used from upstream packages supplied by official Ubuntu server:

linux-headers-4.11.1-041101_4.11.1-041101.201705140931_all.deb
linux-headers-4.11.1-041101-generic_4.11.1-041101.201705140931_amd64.deb
linux-image-4.11.1-041101-generic_4.11.1-041101.201705140931_amd64.deb