Hey PDJ-SF,
We understand that when your iPhone 12 Pro is connected to your home Wi-Fi network for a few hours, Wi-Fi calling will stop working until you restart your iPhone. To clarify, are you able to successfully make calls with FaceTime audio calls or normal phone calls? We want to see if there are any issues with other types of calls.
Also, please try any steps you haven't already from the steps below. The steps are from this article: Make a call with Wi-Fi Calling
If you can't turn on or use Wi-Fi Calling, make sure that your carrier offers Wi-Fi Calling and that your devices have the latest software. Then, follow these steps if you can't turn on Wi-Fi Calling or make a Wi-Fi call. Wait two minutes before you go from one step to the next.
- Go to Settings > Phone > Wi-Fi Calling and make sure that Wi-Fi Calling is on.
- Restart your iPhone.
- Connect to a different Wi-Fi network. Not all Wi-Fi networks work with Wi-Fi Calling.
- Turn Wi-Fi Calling off and then on again.
- Go to Settings > General > Reset and tap Reset Network Settings."
Please note with Reset Network Settings, you will need to sign back into any Wi-Fi network that your iPhone was connected to before, including ones with passwords. You will want to make sure your have your Wi-Fi password if your home Wi-Fi is password protected before doing that step. This will also reset APN, VPN, and other cellular settings.
Take care!