Sensors disappeared

My unit wasn’t talking to my base. I’ve spent 1 hour 40 minutes with tech support. Once they reset the base, all of my sensors disappeared from my devices. They are telling me that I have to re-add each and every sensor to the system. This will take forever! Why is this necessary - we’ve had this system for over a year and the previous owner of the home had it for 3 years. When we bought the house, all of the sensors automatically transferred. Now they’ve just vanished? This in itself feels like a security breach - very concerning for a security system company.