Contact sensor goes offline

I have 1 sensor that, after months of reliability, will not stay online. The sensor is on a door less that 10 feet from an Extender and about 20 feet from the base station. About 10 days ago it disappeared from my managed devices. I had to remove the sensor and take it to the base station to re-pair. The sensor now goes off line every day. I have to manually reconnect it using the app. The battery shows that it is fully charged. I am not impressed that a sensor just vanished from my managed devices and not happy that I have to reconnect it on a daily basis.