The right-hand room never fades out?
Ahhh - I guess I was being dumb and didn't understand the OP... Try this updated version where both sides fade. I used another copy of the Sprite4 as there's no need to use 2 different objects for this purpose.
I've put in 2 event groups that you can enable/disable. The first uses 2 events and no variables and is very simple to implement... The second is 'tidier' to my brain because it only demands the system lerp when fading is in process. Of note on option 1 I had to use a For Each loop - I don't understand why it wasn't detecting the lack of overlap without it...