Knowing how small Snake Island is....and how large an importance it has.....one would think the Russians would be checking to see who might be "looking" when they try a helicopter landing or beach assault of the island.
Logically, it would seem that observation of the island would involve the use of Drones/UAV's for tactical use and perhaps Space based for other uses.
Are the Russians unable to determine the presence of Drones and/or UAV's in the airspace overhead Snake Island?
The video of the Mi-8 being destroyed shows a real short reaction time.....as it shows Troops moving immediately adjacent to the Helicopter as it is being struck by a Missile of some kind.