Plot hole: What on earth are those sailors doing with Hyde when he is chained up on The Nautilus? He is solidly chained to the floor and walls and they keep stepping up to him to allow him to swat them out of the way, risking injury or even death. They stand around like idiots as if waiting their turn to walk up to Hyde and be belted across the room. Why? Why are they even there? Hyde doesn't need subduing, and if he needed guarding they could do it without getting into range.
Suggested correction: They are there to subdue him because he is strong enough to tear the chains from the walls, which he does seconds after they stop trying.
Plot hole: When the team plays back the record, it contains an extremely high-pitched tone which triggers the crystal sensors on the ship. But the speech on the record is low quality. This low quality would be the result of extreme frequencies being lost; but if they were, the trigger tone (a VERY extreme frequency) would be lost too. If the League's gramophones are capable of recording and playing such a tone, they should also be able to record and play back the speech without any quality loss. (01:09:05)
Plot hole: When we are shown the Nautilus' journey into Mongolia, are we expected to believe that this very, very long ship could travel down this river, even though it has a lot of sharp turns in it? (01:15:10)
Plot hole: As the Nautilus makes its way along a canal in Venice, you can see a bridge ahead of it that is far too low for the sub to pass under. Yet without altering its running depth, the sub miraculously appears in the canal well beyond this bridge moments later, and that bridge is not damaged.
Plot hole: When the Nautilus is in Mongolia, we are shown that there is deep snow everywhere. If this part of the movie takes place in July or August, why would there be any snow at all? Even the Yukon doesn't have snow in the summer, except for the northernmost portion of the province. (01:15:20)
Suggested correction: Mongolia is known for wildly changing weather patterns. Sudden snow or hail is common there, they are at an elevated position and is also set more than a hundred years ago.