I found that my slides were working intermittently when retracting. I was always able to get them to work by pushing the "out" button, and then the "In" button a couple of times. However, I became reluctant to extend my slides, especially when boondocking in a WM or a rest area, since the possibility of failure seemed imminent. I discovered that the plastic behind one of the terminals on the slide solenoid was slightly deformed by heat. Apparently, a dirty contact was causing a high resistance connection. I removed the nut and cleaned the surfaces with a wire brush, and I've had no issues since.
"Wire Brush<" you might ask. Because it works.