The Shifts
So, it has been defined that the Backrooms shift overtime, like Level 0 shifting in lore. And if the ancient wanderer civilization "The Lost" came from so long ago, then why are there elevators and stuff? Because it shifted, but that is beside the point.
What I am saying is, whenever a major shift occurs in the Backrooms, it often causes increased chances of no-clipping in certain areas. What did I "solve" via this theory?
The vanishing of the village of Roanoke from the face of the Earth is one major example. Around that time, technology was changing, and the Backrooms followed the trend. This shift then consumed the colonial town.
There are more examples that I will not go into, but I think you get the idea.
Extras
Extra no-clipping stories:
"DB Cooper" hit the ground so hard in the right place he came to the Backrooms.
Same with Amelia Earhart.
Want more? Look up famous disappearances!
What do you think? This may be an early-stage idea, but still.