over the past year, there's been a few times where i notice one of the tiles in my house is blocked. it cannot be walked on and it has nothing on the floor. it also blocks the upper and bottom floors that fall on that same spot, so it doesn't seem like one item hiding. it's been happening for a while and i'm unclear as to what's the cause of this? or how to get rid of it. my only guess is that it's being done by other plays? has anyone else experienced this, know the cause, or how to fix it? i cannot go in to design mode because it is a vendor house (which might fix it).