Iphone 15 Pro Max Bluetooth connection issue with Apple Watch Ultra

My iPhone 15 Pro Max is having an issue with connectivity to the Apple Watch Ultra. It will hold a Bluetooth connection for about 18 hours and then the connection becomes broken. The watch says it is not connected. The phone says it is connected. The only solution to fix this is to restart the phone. This never happened on the iPhone 13 PM or the 14 Plus. I have tried several software updates hoping for this to be resolved.

I have tried:-

• Resetting phone and watch
• Setting up phone and watch from backup
• Setting up phone and watch as a new device
• Resetting network connection

Any advice or help would be gratefully received.

I have an appointment with Apple in the new year, but my gut feeling is there is something wrong with the phone hardware. In comparison, my brother has a 15 Pro with Ultra and does not have any Bluetooth problems.