Episode #4.8 - S4-E8
Plot hole: For things to go the way Goodman describes them, Dwayne and JP must have not heard in the deserted courtroom building the noise of the glass of the fire alarm button being shattered in the corridor just outside their position. It's an impossibility. (00:18:00)
Episode #4.6 - S4-E6
Plot hole: The killer is able to dupe the victim into hiding at the back of a car promising that they will bring a certain someone on a bench and get them to talk about a very bad thing they've been doing, so the designated victim can record the conversation with their phone. This requires the victim to be outrageously stupid; the car, with a closed trunk the victim is hidden in, is parked at distance from the bench; the microphone of her phone would never record that far, and nobody would believe their own phone can work that way, especially when they can hide the phone in a sports bag by the bench, the bushes, the gaps in the bricks or just demand that their supposed friend carries the phone herself. Also, the killer couldn't be sure that the device wouldn't say something about what they were doing (as often happens before you start a recording; you state the time, place, purpose of the recording, plus all the other content of the phone she didn't have time and chance to review!), but makes no attempt to make the phone disappear.
Episode #4.8 - S4-E8
Plot hole: The way the murder happened (where was the gun shot from?) is entirely unknown for the first couple of days, not even a hint - it seems the investigators don't care at all about it, which is quite silly per se. More importantly though, knowing so little about the way the shooting happened would have at the very least prompted an analysis of the shirt to check the entry wound and any residual. During that sort of test the 'other substance' used in the trick would have been easily discovered (visually it is radically different up close and drying out), exposing the culprit.
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.
Episode #4.2 - S4-E2
Plot hole: The police staff in this episode act as if it's morning and they just met; Camille goes fetch her boss at his shack after he barely survived some jogging, and he never asked her about the date she had the previous episode, aka previous night (because of course two murders happen in two days in the little island). But the murder happened in the evening, at least well past 5 PM when it rained. Aside from the fact that the light during the first interview with the suspects is perfect and bright for being dinnertime even in a tropical paradise, what have Humphrey & co. been doing all day, if the day is almost over and they are exactly as we left them at the end of the previous episode?
Answer: Most likely they had only tropical exotic drinks, he wanted an old fashioned English beer.