Entry Sensor "Office" is not responding.

Dead battery is the usual culprit.  If a new battery doesn't help try swapping a sensor from another room.  If the sensor works elsewhere but not in the office then there is some type of interference stopping it from talking to the base station.  If this is the case try moving your base to a better location.

I'll try answering my own question with this:

https://support.simplisafe.com/hc/en-us/articles/360029478532-Sensor-Not-Responding-Warning

Well, I went into test mode, and the Entry Sensor tested fine.  Perhaps missed the first button push, but got all after that.

And the message on keypad of
Entry Sensor "Office" is not responding
has disappeared now.