Door sensor continually going offline

The situation: I have a door sensor that continually goes offline, then will come back online at its leisure. There is no rhyme or reason as to why this occurs. The layout: the sensor is on the man door in a detached garage, approximately 50 feet from the back of my house. The base station is as close to the back wall of the house as I can make it. There is another sensor on the main garage door that is about four feet in front of the sensor that goes offline. This sensor works with no issue. I have replaced the sensor once, from Gen I to Gen 2, and the problem continues. I can't move the base station any closer without putting it outside. Help! I'm so frustrated with this.