Gen2 door sensor issue

One of my door contact sensors went offline. I changed the batteries thinking that was it, but that didn’t work. I read the article on troubleshooting and attempted to do a factory reset and re-add the device. After trying this multiple times, the app still shows the “sensor needs a factory reset”, and it shows “state of sensor unknown”. That’s where I am in trying to re-add the sensor, with no luck. This is 3 years old and have never had this issue.