If it was one zone all the time I would suspect the DS12A or signal path to the console from where it is mounted.
If many are now faulting on problem or open. I would suspect the SC1200A console, but I can not be that certain.
You may want to use the search feature to find other threads on problems but they are all near the top of the sections. So you may just want to look at some of them.
I have seen zone problems, poor RF range, reception problems, answering machine and Powerhorn problems with the SC1200A reported.