I think this is because the value of a reward point is given in $ and not satoshi. I assume 1 RP is supposed to have a valie of 0.0001$ and the corresponding amount of satoshi is being rounded down. As long as the BTC value was above 5000$ this resulated in a value of 1 satoshi, but since BTC dropped below 5000$ it's value is 2 satoshi. You will also notice that the lottery tickes now cost 2 satoshi too and I'm pretty sure it is connected to the BTC dropping below 5000$ value.