Why does my door stop opening when I stop moving?

To save you some trouble: Get Overlapping Actors | Unreal Engine 5.2 Documentation.

The one you were using has two triggers, so the triggers will basically fight each other. They also didn’t trigger at the appropriate times, which could cause them both to fire at the same time.
My graph has only one trigger (the tick) and simply checks the state of the box. It literally translates to “if the player is inside the box, open the door; else, close the door.”