There are several continuity breaks in the film: a brown-haired stuntman can be seen from behind doing stunts for the black-haired Scott, shots from other Scott-Tarzan films are inserted into action scenes, and the handle on Scott's hunting knife changes when some of these inserted shots are close-ups.
In the sequence where Tarzan crosses a raging river, he (and his loincloth) appears entirely dry within seconds of emerging from the water.
Tartu is hacking away at a dugout canoe with a machete as though he has been building it and is just finishing it up. Only problem is, the canoe appears finished and is very weathered and gray in color, but on the very end where Tartu is shaving some wood off with his machete, he is revealing fresh pale wood color that stands out against the rest of the weathered wood. So he is clearly just pretending to be working on an old finished canoe.
During the river journey, the dugout canoe that Tartu had been working on doesn't show the freshly-scraped area on one end where Tartu had been working on it. If it's really the same canoe (and it probably is), then this scene was filmed before the scenes in which Tartu pretended to be working on the canoe by scraping some of the gray weathered wood off of one end and exposing fresh pale white wood underneath.