The most common cause of sensor connection issues is alignment. Make sure that the magnets are aligned to the indicator notches on the sensors and are passing within about 1/8 of an inch or 4 mm from the sensor. The indicator line on the cadence sensor circumvents the end of the sensor while the indicator line on the speed sensor is located to the upper left of the battery.
Try repositioning the magnets and sensors so that they are passing over these lines and retry connecting using our Wahoo Fitness Utility app.
If you still have issues then please remove the sensor from the bike and manually pass the magnet by hand over the sensor to see if you receive any response.