I had a similar problem and then I made sure to carefully disconnect the sensor board then reconnect it making sure the connector cable is fully seated, (make sure you turn off the phone first and probably disconnect the battery as well before doing this).
On the subject of the sensors, I wondered if you or anyone else has utilized the other expansion boards? For instance I want to see the GPS board work, and NFC but I don’t see how I can check if they’re working while attached to the phone. Am I supposed to upload some program for the Duino board itself? And if so does anyone have something to use? I feel silly that I’ve got these expansion boards and can’t use some.
I’ve successfully used the LED matrix and the color LED strip. Works great for detecting high/low temps and changes in lighting.