I'm not saying you're wrong, but this makes for one hell of an unexplainable coincidence: I tried again 30mins after I posted this issue and got the same results (a reboot of the Mac didn't make a difference). So I turned off "disconnect connections after 30mins of inactivity" and it worke...

Viscosity 1.7.9, OSX 10.13.4. First time using Viscosity since the update to 1.7.9, I connect to a VPN and it disconnects within ~15 seconds. I also have Viscosity 1.7.9 running on my Surface (WIN10 1709.16299.431) and it connects and stays connected to the same VPNs. Works great on the Surface. All...