VULTR has recently made changes on their end, and everything should now work fine 'out of the box' with NetworkManager enabled. Should you wish to disable NetworkManager, you can follow these steps.
Pasted below is an example
/etc/sysconfig/network-scripts/ifcfg-eth0 file. This template configures IPv4/IPv6 statically. Substitute DNS/HWADDR/IPADDR/GATEWAY/IPV6ADDR from your existing configuration.
DNS1=126.96.36.199 ONBOOT=yes BOOTPROTO=static DEVICE=eth0 IPADDR=188.8.131.52 PREFIX=23 GATEWAY=184.108.40.206 DEFROUTE=yes NM_CONTROLLED=no IPV6INIT=yes IPV6ADDR="2001:1234:1234:1234::64/64" IPV6_AUTOCONF=yes
Then, disable NetworkManager and restart networking:
systemctl stop NetworkManager systemctl disable NetworkManager systemctl restart network
Don't forget, should you lose access to your box you can use the VNC console from the control panel.