The Turks storm the (empty) ANZAC trenches on the 20th December 1915. The movie portrays this as a sunny day with hot weather. In reality snow and frost appeared as far back as November with as many as 16,000 cases of frostbite and exposure reported for November alone.
The coffee cup that he drank out of was not made until 1955 at least, as it was made by the Belleek factory and the back stamp on it relates it to between 1955-1965.
The dust storm in which Connor rescues his young sons is used to dramatic effect in the movie, but is neither particularly common nor life-threatening in Australia in general or the northwestern area of Victoria where the Connor family were farming. Bushfire and grass fires are a far more realistic and common threat, which most definitely could have caused a dedicated father like Connor to gallop off in search of missing children.
The British Occupation troops in Constantinople/Istanbul are armed with very rough and obvious mockups of the fully stocked .303 caliber Short Magazine Lee-Enfield rifles which were correct for their unit and period. "Giveaways" making the mockups obvious include: wrong bolt action; lack of the large charger bridge on the action; lack of the distinctive protective "ears" on the backsight; two fore-end bands where the real rifles had only one; incorrect buttstock; incorrect profile of the distinctive angled 10-round magazine which projects below the action on real SMLE rifles. Presumably mockups were necessary because armourers could not source sufficient stocks of the correct model of Lee-Enfield rifle in Turkey.
The New Zealand soldier is wearing a lemon squeezer hat with an infantry puggaree and 9th Mounted Rifles Regiment badge. If he was Mounted the puggaree should have a green center and be shaped as a slouch hat.
The British Army Officer Lt. Col Hughes was wearing the rank of Lt. Col but at the same time he is wear red stripes which are worn by Col, who are one step to Lt. Col. This was wrongly show.
On the battlefield, right before Art shoots Henry, Art takes a look at his dead brother Edward.
The first close up of the face shows that the face is completely shot off, including the eyes.
The second close up (a little bit further away from the body) shows the face, but here it is less damaged, e.g. the right eye isn't damaged.
When Conner is digging the well there is not enough debris from the hole he is digging. Ironically, when he digs his wife's grave there is way too much debris from the grave.
Major Hasan tells his troops to "wait for the sun" before charging out of their trench. In the background of the trench in a shot or two later, full sun can be seen and when the men leave the trench it is completely sunny.
In the Galata area aerial overview scene the Galata tower has a cone shaped top, which was not built until the mid 1960s.
Movie shows clearly that Connor enters Istanbul through the port of Haydarpasa (at the Asian side of the city). The boy drags him to the hotel which is supposed to be around Sultanahmet (European side). This is verified by the boy's comment "Sultanahmet, we go!" and with the camera shots several times downhill from the hotel with a clear view of Galata tower from the old city.
The problem is; Connor follows the boy running from Haydarpasa to Sultanahmet in a couple of minutes, which is impossible due to the Bosphorus waterway between the Black sea and the Marmara sea passing through the city.
(They should have taken a boat).
Throughout the movie the characters are naming the city Istanbul, although it changed the name from Konstantinopel to Istanbul in 1930, and the movie took place in 1919.