As it is only Google, it still sounds like you have another device that is giving away your location. If you are logged into Google on a device that is connected to the VPN and one that is not, it could be reporting either of them. For instance, if you have your phone disconnected from WiFi, but still logged into Google, it could be reporting your location from there.
But if other sites are reporting the correct location, it doesn’t sound like a bug or a networking issue to me.