you are constantly changing the start location (A pin on lerp node). when using a lerp with a timeline you need to have two set locations, other wise you get exponential acceleration of sorts.
for your case since your working in local space you dont actually need to get the location of the door. basically your door wil always be in either the open or closed state (or somewhere between the two). so you can just specify the locations and be done with it. what im saying here in its most basic terms is that you can have pin A set to 0 0 0 and have pin B set to where you want the door to end up say 0 100 0. since its local space all locations are based on the actors origin. so even if you move the actor the door will still work the same.
now if you were using world space then thats another story. if using world space then you would need to create a variable and set the actor/components world location to the variable. then you would use the variable as the start location and add a vector like you did in your picture. personally for a door i would use the first example where your working in local space.
