Password AutoFill does not pick up saved password in developer mode

Without developer mode, I was able to get Password AutoFill to work in my SwiftUI app with my local Vapor server using ngrok and adding the Associated Domains capability with the value webcredentials:....ngrok-free.app and the respective apple-app-site-association file on my local server in /.well-known/. (works on device, but not in the simulator).

However, if I use the developer mode (webcredentials:....ngrok-free.app?mode=developer) it only works halfway when running from Xcode: I get asked to save the password, but the saved passwords are not picked up, when I try to login again. Neither on device, nor in the simulator. If I remove the ?mode=developer it seems to work as expected.

Is this by design, or am I missing something?

    var body: some View {
            ...
            Section(header: Text("Email")) {
                TextField("Email", text: $viewModel.credentials.username)
                    .textContentType(.username)
                    .autocapitalization(.none)
                    .keyboardType(.emailAddress)
            }
            Section(header: Text("Passwort")) {
                SecureField("Passwort", text: $viewModel.credentials.password)
                    .textContentType(.password)
            }
            ...
    }