Why did 24 special police officers lose contact?

At noon on September 8, due to weather and terrain factors, 24 people couldn't get through the satellite phone contacted by the headquarters and lost contact before and after. During the rescue mission, 24 special police officers were trapped in a valley or where the signal was off. Without a signal, they can't receive information from the outside world, and they can't send messages to others, which leads to the loss of contact.