At the beginning of the movie when the newsboy is selling papers announcing war has been declared, it's supposed to be April, 1917, but all the women in the scene are wearing cloche hats and short 1930 skirts. When L&H are sitting on the park bench, all the women in the background are dressed appropriately for 1917.
Stan and Ollie are sitting on a bench, Stan gets up causing the bench to tilt up knocking the cook, George Marshall, unconscious. George's hat falls off as he falls but in another shot he'd still got it on.
Whilst in the apartment, Stan looks at a newspaper article referencing the Empire State Building in New York. The Empire State Building wasn't built until 1931, but Stan and Ollie supposedly had just returned from the Great War, meaning the year should have been 1917 or 1918 and the Empire State Building was not yet built.