Are these fare changes - as in a change in price for the same fare rule/or a new fare filed - or are they reflecting fare bucket availability? The former is limited to x times per day by the GDS. Maybe six? Fare bucket availability changes in real time. Somebody buys the last seat on any segment that your search had used and you're pushed into a more costly fare.

Even less significant is a comparison across sites in different currencies. That's not a price change at all.