To me, distance would would only cause impedence to increase, which would lead to missed finishes- not false finishes. However, an intermittent short in the line might cause this. Water in the cable or EMI interference (from a chairlift or something similar) would probably be the cause of this.
Look at your photocell as well. Snow buildup on the sensor might be an issue, as would lense fogging. Emitter/detector alignment would certainly need to be checked, as Alge sensors are pretty sensitive. It's easy for a loose mount to cause alignment to drift. I use a lazer level to make sure I'm more or less dead-on at the start instead of just on the perimeter of aligned. Check the distance between the sensors as well- although it's not as critical in most race venues with a thru beam set as with the reflector style. What about batteries and battery connections? New batteries and clean terminals are also a good place to look.
Other than that, I'm out of my league.