It looks like the voltage is fine at the power supply.
You had sent a photo of 12 volts at a keypad. This tells me theres a problem with the wire, and not enough voltage is making it to the keypads.
Somewhere, probably in the ceiling, and possibly because of rats - there is a problem with the wire.
Please look at pages 99 and 100 of our as-built drawings. The keypad cable is run in one large loop. If you take off all the keypads, you should be able to find where the problem is and cut out the bad section of cable.
Please feel free to call me if you have any questions or need any help.