Debugging long 1-wire line with Raspberry PI
I don't have a definitive answer but when I investigated this topic for my home heating I was sufficiently persuaded by my reading that direct bit-banging on the Pi GPIOs might be problematic due to timing jitter. I found this 1-wire Pi-plus and decided it was worth the investment if it saved me some trouble as it buffers the data electrically and should help with timing accuracy.

Figure 1. 1-wire Pi-plus timing is independent of the Pi.
You may be on the edge of working and the cable capacitance is just pushing you over the edge. This device might help with your troubles.