Other mistake: As the divers prepare to descend to the Roman shipwreck, none of their buoyancy aid inflation valves are connected to an air intake. This makes the rapid inflation, which happens on their ascent back to the surface, impossible. (01:15:15 - 01:15:50)
Other mistake: In flashbacks, younger Indiana Jones has exactly the same voice as the older one.
Suggested correction: Harrison Ford's voice has always sounded the same. Watch any film he's done.
It's a noticeably "older" voice than in previous films when he was about the age his de-aged self is meant to be. I mean he's now in his 80s not 40s, of course his voice is different! An unavoidable mistake but still clearly different.
Actually, it is easily possible to augment his older voice to sound young. If his older voice is too deep, for example, Ford could merely speak slightly slower when recording the dialogue - and then it could be sped up slightly in the final cut. Or, audio AI can be used to alter voice patterns as desired nowadays (ex. To remove the 'gravelly' aspect of his voice).
Harrison Ford's voice has definitely become pretty gravelly.
Other mistake: Towards the start of the film, at the end of the train crash on the viaduct, time seems distorted. By the time it's taken Indy to wade out of the river and walk up its bank, magically a troop of British soldiers appear from nowhere, having entirely and instantly overrun a train full of Nazis? (02:16:01 - 02:16:35)
Other mistake: When the divers ascend from the Roman shipwreck, an odd sort of heat-seeking mini-torpedo or poison homing dart projectile is fired down from the surface. Any idea what this is supposed to be? The henchmen on the boat appear to be wielding a knife, a Luger, and a (wrong for the period) 1986 micro Uzi. (01:10:20)
Other mistake: Whilst swimming towards the Roman shipwreck, the divers appear to be moving at a speed similar to an unrestricted diver wearing flippers. The drag resistance from the air pipe umbilical, together with the divers' lead boots, would make this an unfeasible maneuver in real life. Equally, the divers have no BCD or method of maintaining equal buoyancy and would sink to the seafloor - not swim like a fish. (01:13:14)
Other mistake: Dive boat interior, as the tablet is unboxed, there is a clear lens distortion as Indi looks round to his diver friend and the focus follows - giving a disturbing jolt to the image. (01:08:27)
Suggested correction: It just appears to be the result of the movie doing a slightly unconventional rack focus. I don't think that really qualifies as a mistake. If it does count, it opens far too big a can of worms in terms of various camera techniques being considered "mistakes."
Other mistake: In Tangiers, Indy's cab pulls over in front of the mob-owned hotel where the famous illegal auction is taking place. It's dark outside, but when we see Indy in the hotel, and more evidently when they get out of the hotel and the car chase starts in the span of 5 minutes, it's broad daylight. That also means that just before 6 AM (when dawn would take place in August), the hotel is chock full of normal people boozing, playing cards, plus an assembly of rich baddies from all over the world who just happen to wait to have an auction.
Other mistake: The US forces that apprehend Voller in Tanger carry modern-day M4 carbines. These weren't in use until the early 1990s. While similar weapons (XM177) were in limited use in the late 60s, the troops sent to apprehend Voller would much more likely have had regular M16s or WW2 M1 carbines.
