I think the key bit of information here is "misting several times a day." You are creating a major fluctuation in humidity that may not be consistent from day-to-day. If one pitcher has been consistently misted more than others while developing and then, perhaps, you don't hit this same pitcher quite as much or forget to mist, the lid may open prematurely. Although I mentioned humidity, the real issue is conditional changes. Almost every example of pitchers opening prematurely that I have seen result in changes of some kind, whether due to repotting, moving the plant, or abnormal fluctuations in humidity or temperature.
As JB and Don mentioned, the frequency at which you water the plants, coupled with misting and high humidity, could be causing issues with water absorption. Is there any sign of yellowing on the lamina? Do you grow your plants in an enclosure or an open area? If your plants are being kept this wet around the roots and shoot, while being kept in an enclosed system without CO2 supplementation, it is much more difficult for the plant to assimilate photosynthetic carbon and therefore pull water through the xylem tissue via transpiration. Your plant is essentially surrounded by more water than it can use and will divert its energy to more pressing issues than pitcher production.