Now I’ve watched the vids. Thank you Sir for the videos.
These are the questions that came to my mind while watching this:
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How come you didn’t need to have all the “get actor location” stuff that the other tutorial sets up with with “event begin play” checking the door positions all the time?
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What’s the difference between “Set Actor Location” vs the “Set Relative Location” as you used?
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How did you get the program to understand the difference between “locked” and “unlocked” when you made the custom events that went into the false/true branches?
Then as a general feedback to the videos:
A) You haven’t linked the wrap-up video anywhere. 
Just as a heads up
B) While you technically solved my problem, I still can’t have a specific trigger box that will lock/unlock the other door, which would be useful for making e.g. puzzles.
C) You could have mentioned that I did follow a tutorial when I did this in such a wrong way. 
But again, I really appreciate the fact that you took your time to record this just to help me! This really proves how great the UE4 community is
Before I make new door, could I use the “mess” I have and make that lock/unlock mechanism work?