I am using Unreal 4.17.2 and the door opens on its own I have watched this lesson and the three before it multiple times to see what wrong. All the code is the same in the videos if someone could help me it would be a huge help. 
I’m Getting the same problem. Not sure what the problem is but once the door opens and I wait it won’t close with the same code in 4.17.
I did end up getting it to work but it was simply me not saving before building the code.
For me the issue was that the rotation vector for closing the door actually was opening it (because i had my door on a different wall it needs a different angle). The close door function as written runs every tick as soon as the the time passes LastDoorOpenTime. I also added a bool to check if the door was open before closing it.