Why are my realtime PCR amplification plots hook-shaped?

During the late phase of PCR, as a lot of PCR product has been generated, there is strong competition between hybridization of the probe to the target strand and re-association of the two complementary product strands. For some primer–probe combinations, re-association occurs more quickly than probe hybridization towards the end of the PCR. Therefore, the yield of PCR product seems to decrease after reaching a peak. For accurate quantification, fluorescence data is measured during the log-linear phase of the reaction, i.e., during the initial increase of fluorescence, before this phenomenon occurs.