Incoming call notifications problems

Good day

We developed a simple swift code to make the device ringing when a certain type of notifications arrives from our backend. This is the code:

                let phoneNumber = CXHandle(type: .generic, value: (self.userInfoForPluginCall!["data"] as! [String:Any]) ["caller"] as! String)
                callUpdate.remoteHandle = phoneNumber
                
                let configuration = CXProviderConfiguration(localizedName: "Trec Conf")
                configuration.maximumCallGroups = 1
                configuration.maximumCallsPerCallGroup = 1
                configuration.supportsVideo = false
                configuration.supportedHandleTypes = [.generic]
                configuration.iconTemplateImageData = UIImage(named: "callkit-icon")?.pngData()
                let callProvider = CXProvider(configuration: configuration)
                callProvider.setDelegate(self, queue: nil)
                
                callProvider.reportNewIncomingCall(with: callUUID!, update: callUpdate, completion: {error in})

We are noticing some problems on the call screen: on certain devices (iOS 18.4RC) the normal call screen appears and the user can answer or decline the call, on other devices (iOS 18.3, especially with dynamic island) only a phone icon appears in the upper right corner and no possibility to answer or deny call.

Any idea on why we are encountering that behavior?

Thanks