Stupidity: When the trolls are trapped in Chef's cage, Smidge is small enough to slip through the bars and could've easily escaped.
Stupidity: Jake uses several Loops and travels all over the world in order to get back on the boat at the end of the film. This was completely unnecessary as only the final Loop in 1942, which was available to him in 2016, was the one he needed to enter despite the fact that its nature should have prevented him from reaching 1943 anyway.
Stupidity: At the end of "You're Welcome", Maui puts Moana in a cave and placed a large rock blocking the only known exit. This means, as far as Maui knows, he's trapped a human in a cave with no food, water or exit as he didn't know Moana could make a very lucky escape. Basically Maui was going to leave Moana to starve to death so he could take her boat.
Suggested correction: This isn't a mistake. Maui doesn't care about anything other than escaping at this point. He even says, Without his hook he is nothing. He's not interested in returning the heart at first so even though he is a demigod, he has lost interest in being good. Another example is when he leaves Moana to face TeKa on her own.
Stupidity: Gus is a blatant example of Deus Ex Machina. 1: The % of his pod malfuntion was too low. They mention multiple times how low the chances of a pod malfunction are (Jim's is the first in history), and then it happens twice? Jim's med-scanned him but Gus' didn't (?) so he had 610 things wrong with him. So he woke up dying 2: Gus' existence has only one objective: to give Jim the armband. 3: Before anything else can happen with Gus, he dies conveniently. Gus' existence had no other reason. We didn't care about him emotionally. He didn't advance the plot. He provided no new info or answers to questions. (failure cascade is easily discernible by Jim once he has access to the bridge) It would have been easier to just let Jim find an armband/access another way. DXM: holder of the macguffin magically appears (pod failure) delivers the macguffin (armband + code) goes away (dies without explanation) it's downright shameful.
Suggested correction: This is all your opinion of a plotline - admittedly, an utterly lame one - not a film mistake. Film criticism and error spotting are two different things.
In addition, the statistics about pod malfunctions obviously referred to spontaneous malfunctions, which had never happened. These malfunctions in the movie, however, were not spontaneous – they were caused by catastrophic failure of the ship itself due to an asteroid hit.
Stupidity: In a flashback scene, a mother, father and daughter are taking pictures of Norm and two other polar bears. The daughter decides to run up to the three polar bears, but the parents appear to do nothing about it. The polar bears could have been a threat to their daughter for all they knew. (00:04:25)
Stupidity: Long after the Marine Life Institute has closed for the night, the recording of Sigourney Weaver welcoming visitors is still playing.