In fact, this is the only case like this I have seen in 25 years of analyzing comet light curves. This light curve is based on 27 observations made by the author. The plot shows that this comet was quite variable in brightness. This was primarily due to the activity of one major jet. The comet also had a significant fading around -557 days.
Comets can vary in brightness on short time scales.
However, Hale-Bopp varied much more than the average comet during this period. During the last two months of observation, the comet's brightness fluctuations began to settled down. In the third plot, the effect of the changing Earth-comet distance has been removed so that the intrinsic brightness of the comet can be studied. This intrinsic brightness is called the heliocentric magnitude. For example look at the blue line.