Blurry texture behind parts of mesh

Whenever I render my scene with Render Blender, I get this weird blurry box behind the Skyrim Armor I imported in. I didn’t really change anything since the last time I was rendering, messing a bit with mirror was about the only thing I changed. I had been rendering just fine with and without a DoF node but just now it started with this weird blurry rectangle. Any idea what’s causing it/how to fix it?