Chapter 8: The odometer in Billy's car in several shots does not move.
While chasing Betty along the top of a dam, the bad guy is confronted by Captain Marvel; he fires seven shots out of his six shot revolver at him.
Wires can be seen supporting Captain Marvel in all of his flying scenes.
In chapter 11, "Valley of Death" one of the tribesmen uses a signal mirror to communicate with another. He flicks it up and down, but the reflection hits the other in a side-to-side motion.
In Chapter 11 as Captain Marvel heaves a tree trunk from the road way, a crew member steps out from behind a large rock and, realizing his mistake, steps back out of sight.
The setting of the opening and closing chapters is stated to be Siam, the kingdom later known as Thailand. In fact, it is a creation of the writers' imagination, with very little connection to actual Siamese culture. E.g., there are British Imperial troops stationed there, but Siam was never a British colony. It is essentially British India, with some elements of Arabia and Egypt mixed in.
While a prisoner of the Scorpion, Betty manages to grab a gun and fire a shot that creases the villain's hand. Informed of this, Billy manipulates the expedition's members into showing their hands, and only one man's hand shows an injury. However, subsequent events prove he is not the Scorpion. How the real villain had no injury is never hinted at, and there's precious little said about the wound that was found: After Billy escapes a death trap at the latter man's home, the two have a conversation that is joined in progress, with Batson admitting that he could believe the scientist's story (told completely off-screen) about the cause of his injury if he could explain other things that had happened. Perhaps that trap was originally intended to be a chapter-ending cliffhanger and the explanations were lost in re-editing to eliminate a chapter here.
Since there is no stated time limit to his powers, and no mention of his having any Kryptonite-level weakness, why does Captain Marvel bother changing back to Billy Batson at awkward moments which leave him vulnerable to the villains?
At several points, the villains gag Billy Batson's mouth when they tie him up, even though there is no one for him to shout to, and they do not know that his voice can magically summon Shazam.
When Shazam tells Billy about how pronouncing his name turns him into Captain Marvel, he doesn't tell him that, as Captain Marvel, pronouncing his name will turn him back to Billy Batson.