VPN connection failed because service stopped unexpectedly

This might not answer your question, but check if the option in the 3rd pic is enabled. If not enable it & connect again.

I am using Linux Mint 19 and it work for me.

1. Disable your firewall (sudo ufw disable)
2. Disable your ipv6

For Red-Hat system :

sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1

sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1

For Debian system :

sudo nano /etc/sysctl.conf

Add the following at the bottom of the file :

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

After all, restart your machine.