I had a SIG mayhem and I snagged the elevator on something causing the servo to over-extend. It checked out fine so I flew it and, for short periods of time, I had no elevator. Brought it back and realized I had stripped a portion of one of the gears which would only become a problem periodically. I was lazy about it for a while and flew it knowing that when I lost elevator, I had to cycle the elevator servo a couple of times to get away from that bad area of the gear.

I replaced it a few days later, but it sounds like a similar situation....partially stripped servo.