The Kaiser is not wearing the correct decorations. Apart from the fact that he is wearing ribbons rather than medals (Wilhelm II. generally preferred medals to ribbons), one can actually see two of those ribbons sporting swastika-bearing eagles - clearly recycled props from a WW II movie.
Throughout the film, a number of vehicles are shown with pneumatic tyres. Although it is quite feasible that the Kaiser's ca would have had these, for comfort, all military vehicles of the period were equipped with hard rubber tyres, on both sides of the war.
When the newly graduated troops are entraining, a piece of incidental music is played, which is based on the 'Deutschlandlied', the modern German national anthem (think Deutschland Deutscland über alles, although this first verse is no longer sung) is played, but this wasn't adopted until 1922. The Imperial German national anthem from 1871-1918 was actually 'Heil dir im Siegerkranz', which nis sung to the same melody as 'God Save the Queen'.
During the scene with the French flamethrower team when Leer is trying to drag the dead Liutenant to cover, the Liutentant moves his left arm out from under him and turns his head when Leer is tugging at his Y-straps.
In one of the last scenes in the movie, Paul is shown walking with Katczinsky carrying a bucket of turnips in his right hand. An artillery barrage comes and Katczinsky runs to the left while Paul drops the white bucket (and spills the turnips) and dives into tall grass on the right. The camera quickly cuts to Katzinsky showing his wounded leg, then cuts back to Paul, who stands up and runs over to Katzinsky. When Paul runs over to Katzinsky, the white bucket and the turnips are no where to be found.
After the scene when Leer dies it shows the Germans in their trench and they all have mud on their helmets. It then shows Westhaus and his helmet is clean, but it is muddy again in the next scene when he is shot exiting the trench and falls back into two of his fellow soldiers.
In the scene of Kaiser Wilhelm pinning medals on the soldiers, the battalion is at "Present Arms". In the very next scene, the battalion is at "Attention" (rifle butts resting on the ground), without the command "Order Arms" having been given.
When Himmelstoss arrives with his new platoon, his old trainees tell him that Kemmerich is dead and he crosses his arms in front of him and says he doesn't remember him. In the next scene, his hands are clasped behind his back instead of crossed in front.
When Corporal Himmelstoss arrives to the front and is welcomed by the main platoon. He commands his new platoon to march away and as they are doing so there is a crew member seen right behind the cast in the top left corner.
Corporal Himmelstoss' rank is indicated in the movie by his shoulder straps. In the World War I-era German army, a Corporal's (Unteroffizier's) rank was indicated by lace trim around his collar and cuff.
Kaiser Wilhelm's staff car is missing the Kaiser's personal pennant. Being a stickler for protocol and enormously fond of parades, it is highly unlikely that Wilhelm II. would have attended an official function (particularly an award ceremony) without the proper paraphernalia.
The rifles used by the German soldiers in the film are model 1903 Turkish Mausers, in reality they would be using the German Mauser Gewehr 1898. The bayonet is also the Turkish 1903 pattern, which is distinctly different from the German model.
The Kaiser is merely wearing the rank insignia of a Generalmajor (Major General) - plain shoulder cords for general officers. Wilhelm II. always wore the rank insignia of a Generalfeldmarschall (Field Marshal General), which were the shoulder cords for general officers with two crossed Field Marshal's batons, a crown, and the initials "WR" ("Wilhelminus Rex" = "King Wilhelm").