When Lieutenant Harp phones to his old command and speaks to the other drone pilot, she identifies herself as Corporal Bale. If she were in the Air Force, she would have identified herself as Airman Bale, perhaps Sergeant, where most of the branches merge in identification. By identifying herself as Corporal, she's not in the Air Force.
Harp wears a plate carrier vest (body armor) for most of the film, but it obviously does not contain any plates as it is too thin and flexes while he walks. Since there are no pouches on it to carry ammo, radios, first-aid or any other gear, it is useless for him to be wearing it at all.
On two occasions, a drone fires one missile and completely destroys a building. This happens first when attacking the bank and then, at the end, when a single drone fires a single missile and destroys the factory.
Drones mostly carry Hellfire missiles, which are anti-vehicle missiles. They don't carry an amount of explosives that will bring down a house, let alone a whole complex. However, the story takes place in 2036, and new technology could have produced a significantly more destructive missile.
At the beginning, Harp states that he trained at Parris Island. This may not be a mistake. While Air force basic training occurs at Lackland AFB in San Antonio, job training can occur at any domestic military base, with some training occurring at bases that are not controlled by the Air Force. Harp probably completed basic training at Lackland, but he then may have gone to Parris Island for drone training.
Opening scene says there's a war in Eastern Europe, but the map shown (including the coordinates) is Palma De Mallorca, off the coast of Spain.
The drone view displays the coordinates 49° 27' 08.9" / N 32° 02' 29.0" E when approaching the nuclear missile silo across the Russian border. These coordinates actually point to a residential area in Cherkasy, Ukraine.
Following the final explosion, the view from the drone on the big screen is mirrored. All other views are the correct orientation.
When Leo takes Viktor hostage and kills all of Viktor's supporters and guards present there one by one, there was enough time for any of them to shoot and kill (harm) Leo. Leo can and does only shoot them one by one, there were more than a dozen, but it seems they kept waiting for their own turn when Leo turns to shoot them, only then they would try to shoot Leo. So, instead if all of them had got alarmed as soon as Leo captured Viktor and shot at Leo simultaneously, Leo would have been dead.
Leo claims Harp has "56,000 flight hours". To amass that many flight hours, Harp would need to fly 12 hours/day for 13 years, with no days off. Harp has only 3 years of service.
Several times Ukraine is referred to as "The Ukraine". This is a common mistake. The use of the article relates to the time when Ukraine was a republic of the Soviet Union known as "the Ukrainian Soviet Socialist Republic". Since then, it is merely "Ukraine".
Marines address each other as "soldier" multiple times in the film.