i got a bee house from one of the community center bundles and i had it sitting outside of my house and now its gone.
There's a few ways a placed object can be removed from a farm. If a weed spawns on a tile it'll overwrite whatever was there. Paving underneath placed objects will prevent this. Lightning strikes will destroy objects if it strikes one. Lightning rods will prevent this. If an object is placed in the path of an npc they will destroy it to move forward. This is unlikely on the farm itself.