Air carrier Captain reported the proximity or distance sensor of the AccuPark system guidance at LPPT/LIS remote park stand 412 was malfunctioning and preemptively stopped to get assistance from ramp personnel.

Narrative

We lined up with the AccuPark system [at remote park stand 412]. Lateral information was being provided via the equipment; but my First Officer and I; noticed to be extremely sensitive. As we continue to approach and still within a reasonable distance; we observed that the proximity or distance sensor was still indicating full; sensing light display 'too far;' and as we continue to approach; we noticed that nothing changed. We were wondering; and taxiing forward very slowly; until we finally decided that continuing to move forward could pose a risk to safety; and that something was not right so we stopped; set the parking brake look to my left. There were few customer service representatives on the ramp; but they never indicated that we were passing the point at which we should've stopped.I indicated with hand signals to them that we would not move and the parking brake was set. When ramp personnel connect the headset; he told me we need to be pushed back slightly; to the parking position. Airplane was slightly pushed back about 6 ft. Doors were finally open and deplaning continued as planned. According to the personnel on the ramp; this problem had already happened the day before; and the airport authorities did nothing about it.