Phone VPN connection to pi-hole behaving oddly.

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So I have Pi-hole and OpenVPN setup on a raspberry pi on my home network. I created a .ovpn file and put it on my phone, for use when I'm away from home. Normally it shows up in the pihole interface as phone.vpn, under the same IP address as usual. However today for ~2 hours in the middle of being used, the device showed up as a different IP address, before later returning to the same one as usual. I was just wondering why this has happened, as it's never done this before, and I was confused as to what the "new" device connected to my network was.

Thanks for you time.