Problem with CO1224T Carbon Monoxide sensors

So i just replaced my 3 Carbon Monoxide sensors, System Sensor CO1224T. After i installed them, I after about a week or two, I got a trouble notice. "AlarmRelay Notification: Protection Loop Fault - Zone 0XX". It seems that after I reset the panel, it goes away, but eventually comes back.
 
The other day, i went through all the wiring to make sure everything was tight. Checked the resistor and it checked out. double checked the way i wired it. Turned everything back on and it was fine for a few weeks. then the code comes back.
 
As I mentioned earlier, this was a replacement, not a new install. Never had problems with the older sensors.
 
Does anyone know if there is a way to isolate a problematic sensor? The lights seem normal. The only thing I can think of is that I have a bad wire somewhere in the wall. We have had mice issues and thought one might have eaten through a wire.

So just got off phone with SS. I checked voltage on power side. getting approximately 13.89V; CO require min 10v to work. Checked resistance of monitor circuit at control and measure 2.19 which equals the resistor by itself, so that seems to function (this was after replacing the resistor). All the COs are flashing the green once per minute which seems to be normal operation; SS confirmed that if one unit was bad it would flash red.
 
This is leading me to believe that there is a problem with the mother board on the M1G. We have had a few more false alarms than normal on a few motions. I thought it could have been rat/mice or spider. Maybe related? Anyone had similar issue to this?

Can you switch the detectors to a different zone and see if the problem moves to the new zone?
 
How old is your M1's battery?  When the M1 does the battery test once per day, a bad battery might pull the supply voltage down to the point where it causes a problem.
 
Are the CO detectors powered from the M1's power or an aux power supply?