I use a VPN, and I'm constantly disconnected from it, whether I use the VPN developer's own application, or GNOME's OpenVPN. It will connect successfully, and then a few seconds/minutes later, I will be disconnected. I have actually tried using two different VPN providers, and the same thing happens with both: Private Internet Access and Mullvad.
Pure OS is up-to-date; I've run apt-get update && apt-get upgrade, and I'm told as much.