Just encountered this too - looks like the parameters to the delegate have changed, so where before your handler definition would have looked like:
void HandleControllerPairingChanged(int GameUserIndex, const FUniqueNetId& PreviousUser, const FUniqueNetId& NewUser);
Now it should use the FControllerPairingChangedUserInfo type like:
void HandleControllerPairingChanged(int GameUserIndex, FControllerPairingChangedUserInfo PreviousUser, FControllerPairingChangedUserInfo NewUser);
And any code inside the handler that used to directly read PreviousUser / NewUser as a FUniqueNetId now can access the same value through the struct’s User property, so PreviousUser.User / NewUser.User.