Motion Sensor Not being detected

I've been a SimpliSafe customer for about 3 years and recently got a message that one of my motion sensors had not been responding.  I've had this happen before and found that removing the sensor From the system then reconnecting it solved the problem.  This time, I tried the same thing with no luck.  So I put a fresh battery in and tried re-installing the sensor with no luck.  I moved the sensor close to the base and tried installing it with no luck.  Does anyone have any suggestions?

Thank you,
John