Episode #4.3 - S4-E3
Plot hole: Five people in total are on a remote location, but they have food poisoning, so severe that they call in the paramedics. Humphrey arrives when they are being taken care of already. During all the time it took for the doctors to arrive, and when the actual rescue was there and was administering help, nobody bothered to check on the victim in his tent - if anyone did, they would have found him dead, since the poison killed him in 30 minutes. The son, the lover and the good friend of the victim, nobody thought about him for a moment.
Episode #4.3 - S4-E3
Plot hole: The killer poisons the victim's belonging when they met early in the morning - that means that the victim stayed the whole day with the poison in the pages of his journal he always brings with him. Yet the murderer's plan required the poisoning to happen at a very specific and precise moment: the end of the day after they'd all had eaten together the stew with the non-lethal dose. It is something that they couldn't have planned at all the way it is described, not when they did the poisoning so far in advance.
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
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