When the island is first seen through the spyglass, after his conversation with Friend, the captain orders to prepare to weigh anchor. As the ship is already moving, the order is wrong, as weighing anchor means to raise the anchor from the sea floor and hoist it on board. The correct order would be "prepare to anchor", but even then, the ship is too far away for the order to make sense.
At 32:30 in the movie, the main character writes the date September 2nd. He had at least been on that island 2 days and was at sea 67 days which put the date he left at Jun 25. Earlier, he showed a newspaper that said the Archduke Ferdinand had been shot. Archduke Ferdinand was shot on June 28th.
When Friend sees the ship off the coast, he runs and grabs the flare gun and runs down to the beach when he should have gone to the highest point. The top of the lighthouse.
The protagonist, a Brit, uses a Russian Mosin-Nagant military rifle.
It may have been used as a stand-in for the similarly looking British Lee-Metford rifle, a likely choice to equip someone in his position.
When Gruner tells Friend that "We need more timber", there aren't any trees on the island to get timber (or firewood) from.
When the creek, or spring, is seen for the first time, the stream of water (that is supposed to have been there for hundreds or thousands of years) is just beginning right then.
Friend talks to himself about the "strange beings" possibly having antifreeze in their blood. Antifreeze did not become readily available, let alone common knowledge, until the 1920s.
The lighthouse has a wall clock which is briefly seen near the beginning, then seen again longer later. Such a clock did not exist in 1914. Large clocks then were larger, more complicated, and did not have such modern numbers on their faces.
The nameless British man wears a world war 2 Wehrmacht m40 greatcoat.
The Moon appears in the sky as it would in the northern hemisphere, but it should be inverted, as the film takes place on the edge of the Antarctic circle.