Regression: OpenVPN plugins fails to keep connection alive

After a few minutes of inactivity, the VPN gets disconnected. In the log extract below, the key part seems to be this one:

Oct 5 11:51:30 tadzim3 nm-openvpn[1526]: WARNING: Failed running command (--up/--down): could not execute external program
Oct 5 11:51:30 tadzim3 nm-openvpn[1526]: Exiting due to fatal error

Here is the full extract:

Oct 5 11:51:23 tadzim3 nm-openvpn[1526]: [cali-fw-vpn] Inactivity timeout (--ping-restart), restarting
Oct 5 11:51:23 tadzim3 nm-openvpn[1526]: SIGUSR1[soft,ping-restart] received, process restarting
Oct 5 11:51:28 tadzim3 nm-openvpn[1526]: WARNING: No server certificate verification method has been enabled. See http://openvpn.net/ho
wto.html#mitm for more info.
Oct 5 11:51:28 tadzim3 nm-openvpn[1526]: NOTE: the current --script-security setting may allow this configuration to call user-defined s
cripts
Oct 5 11:51:28 tadzim3 nm-openvpn[1526]: TCP/UDP: Preserving recently used remote address: [AF_INET]186.103.161.74:25402
Oct 5 11:51:28 tadzim3 nm-openvpn[1526]: UDP link local: (not bound)
Oct 5 11:51:28 tadzim3 nm-openvpn[1526]: UDP link remote: [AF_INET]186.103.161.74:25402
Oct 5 11:51:29 tadzim3 nm-openvpn[1526]: [cali-fw-vpn] Peer Connection Initiated with [AF_INET]186.103.161.74:25402
Oct 5 11:51:30 tadzim3 nm-openvpn[1526]: Preserving previous TUN/TAP instance: tun0
Oct 5 11:51:30 tadzim3 nm-openvpn[1526]: /usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper --debug 0 1515 --bus-name org.freedes
ktop.NetworkManager.openvpn.Connection_18 --tun -- tun0 1500 1558 10.8.1.2 255.255.255.0 restart
Oct 5 11:51:30 tadzim3 nm-openvpn[1526]: WARNING: Failed running command (--up/--down): could not execute external program
Oct 5 11:51:30 tadzim3 nm-openvpn[1526]: Exiting due to fatal error
Oct 5 11:51:30 tadzim3 systemd-networkd[616]: tun0: Lost carrier
Oct 5 11:51:30 tadzim3 NetworkManager[823]: <info> [1507215090.1043] device (tun0): state change: activated -> unmanaged (reason 'unmanaged', internal state 'removed')

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: network-manager-openvpn 1.2.10-0ubuntu2
ProcVersionSignature: Ubuntu 4.13.0-12.13-generic 4.13.3
Uname: Linux 4.13.0-12-generic x86_64
ApportVersion: 2.20.7-0ubuntu2
Architecture: amd64
CurrentDesktop: GNOME
Date: Thu Oct 5 11:59:28 2017
InstallationDate: Installed on 2015-01-23 (985 days ago)
InstallationMedia: Ubuntu-GNOME 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
SourcePackage: network-manager-openvpn
UpgradeStatus: Upgraded to artful on 2017-06-15 (112 days ago)