Corrected entry: Sure, they say you should never question time-travel logic in a comedy movie. But when the friends that decided to get in the hot tub at the end return to the present, their future has changed. However, Lou acts like he hasn't seen them since then. This obviously cannot be: if they weren't there up until the point they returned, they wouldn't have had any of the things they returned to. Sure, they changed the future through their actions, but they'd need to be there for the next 20 years in order to maintain those changes. And they couldn't have existed, and replaced their present selves when they returned, as their present selves wouldn't have gone to the Kodiak Club anyway, since Lou wouldn't have tried to kill himself, so their present selves wouldn't have gotten into the time machine in the first place. Deep.
Corrected entry: The delay in the group's realization that they have traveled through time is implausible. Someone in the group would have encountered a mirror before Lou finally does shortly after Phil shows up with their luggage. Additionally, on their way to go skiing, they would have noticed that the lodge's rundown condition would have improved significantly overnight.
Corrected entry: At the start, the Bellhop acts like he doesn't know the gang, and they act like they've never met him. Yet, we later learn that they had some significant run-ins with this guy many times and are regulars at this place, to the point that in the new future the guy is almost a friend of theirs. Plus, the gang is surprised at his one arm, yet they knew about it and how it happened as they saw it. The only thing affected by what they changed is that he had it reattached.
Correction: Have you ever thought that at the beginning they weren't that special to him? They only had the amount of run ins that they did because they went back in time. Also, they only witnessed him losing his arm because they went back in time.
Corrected entry: When they are in the year 1986, a man is seen with a cell phone. The first cell phone wasn't released until 1989 by Motorola.
Correction: Incorrect the first cell phones were around since the late 70's and the earliest cell phone in the US, the Motorola DynaTAC, was released in 1983.
Corrected entry: Lou, after staying back in time, forms a group that is supposedly Motley Crew, name of his group is Motley Lou. Motley Crew formed in 1981, well before 1986.
Correction: The whole point is that Lou drastically altered the timeline to his (as well as his friends') personal benefit; while it may be outlandish that Lou actually replaced Vince Neil (Motley Crue's frontman) in 1986 and changed the band's name to Motley Lue, it's all part of the joke.
Corrected entry: When Nick is in the "Sup Dawg" place, he gets a call on his IPhone. When they go back in time, he is on the ski slope (trying to get a signal) with a flip phone.
Correction: Lots of people have and carry more than one cell phone.
Corrected entry: When John Cusack's character goes into the basement to chat to his Nephew, he says "c'mon you're 20 years old, get out and live life" (or something like that) when they go back in time his nephew is conceived in 1986 meaning that the present must be 2006 but when they get back into the tub to travel back to the present, the readout on the tub says 2010, where the nephew would now be 24 if he had been conceived in 1986.
Correction: It is a character mistake, and a pretty common one in real life. If you put a gun to my head, I couldn't tell you my nieces' exact ages, all I know is they are their 20s. It's not illogical for Cusack to just say he's 20, meaning *in* his 20s if he can't immediately recall his exact age.
Corrected entry: After being transported to the 1980s, the guys have possession of things which they did not take into the hot tub with them. Nick has his cell phone, Jacob has his snowboard, Lou has his backpack, and they are all wearing clothing that they brought with them when they go skiing.
Correction: This isn't a mistake, it's a plot point. They need the Russian energy drink to get back to the present.
I feel this is more of an excuse than a correction.
Correction: This is common in similar types of time travel movies. In X-Men: Days of Future Past Wolverine goes back in time, and stays in his younger body. When he finishes his journey at the end, The Professor welcomes him back, because until that moment, he hadn't returned from the past, but his body was there the whole time living his life. The same could be said for Jumanji: Welcome to the Jungle. When Alex is returned from the game back into the 90's, He remembers everything, but his teammates wouldn't have been born yet. He had to wait until they returned from the game before they would know who he is. They also didn't recognize his parents house, because they remember it being rundown (freakhouse). So, in HTTM, just like they replaced their bodies in the past, they basically just jumped back into their future bodies to resume their lives.