@Privacyplease I think you're jumping to conclusions here. A change for just you doesn't indicate a change on GrapheneOS that has leaked this IP address. I just checked what my results were on dnscheck.tools using Vanadium on my own up to date phone running GrapheneOS (obviously) connected to my mobile carrier and without a VPN, and no private IP is listed like what you're describing is happening on your device. For me, the only one that's listed is the public IP, as expected.
If the cause is GrapheneOS as you claim, then I'd see the address, same as you. I don't know what the cause would be, so I'm only guessing here, but I would imagine that you seeing that address is due to a change made by your carrier.