Is your computer still connected to something when you used the cloned MAC? Cloning the MAC address of a device that is still communicating with the network leads to problems. It might not explain everything, but at least why the connection is more bad then.
Since the ping here is already terrible sometimes, this might be the main issue. High latency on the unencrypted non-VPN connection will cause much trouble on the VPN one.
My next steps would be:
- Testing a VPN server in Mexico
- Checking the logs
- Trying to figure out why the ping to 1.1.1.1 is sometimes >200ms