It genuinely happens. I used to run some networking cables through the walls and forgot one went up into the loft where an old machine was! For a while I was using this machine and couldn't figure out where on earth it was hiding - it didn't help it was covered in the loft! I only remembered it was still at my parent's place after I moved out - I think they even changed router several times but plugged it back in thinking it was something like a printer or extender or something.

An old friend had a house where it was as if his room was built within a room, so there was some gap between his inner wall and and outer wall. He used to crawl around it and hide his servers there.