Had some issues with safedock during fog at LGW last week. We are not supposed to turn onto stand unless we can see it is switched on with relevant aircraft type showing, as it can screw up the guidance.
As we approached we couldn't tell whether it was on or not. This was because the info was just too blurred (not just my declining eyesight, as F/O couldn't tell either).
On one occasion we were taxying onto stand when safedock suddenly told us to stop (far too short). Looking back, I knew I was short of the mark, but still hit the brakes a little too hard in response to the stop sign, all this while the CC are stood up disarming doors. We were eventually marshalled onto stand.
Never had any issues with the old fashioned systems.