good day mate! i had a not identical but kinda similar issue when playing in multiplayer where my base's room that were previously recognized as "interior" suddenly becomes "outdoors" when i log back in. i am not 100% this will work in your situation, but can you try creating walls around one tile (wall frame will do actually) make sure it has a roof on it, then enter that one enclosed tile (it should register as "interior"), then enter your base?
this solved my problem. all rooms i made that were "outdoors" became "interior" once again.