Terraria Housing Glitch

In this Terraria screenshot you can clearly see my castle working just fine filled with npc's living in the rooms. Shortly after it was taken, and I'm not sure what caused it, every room in the castle started saying "This is not suitable housing" and all the npc's left.

I tried researching what could have caused it and it appears it has nothing to do with any of my recent changes.

So all though I hope someone has an answer to this bug, mostly I just wanted to say look at my awesome castle I built :).