Is it necessary to discuss with the fiancée her staying up late and her coldness in communication, or is it better to stop communicating with her until close to the wedding date?

First, you should communicate with your wife without harboring ill suspicions or seeking out faults. You should strive to remedy the coolness and boredom in your relationship so that love and intimacy may return between you. What helps in this is adhering to Allah's command, cooperating in His obedience, purifying intentions, and relying on Allah.