Some parts of the model just dissappear, kind of like booleans in a 3d model program

Im making a game where its just a room and some models and you can control gravity and interact with floating furniture. But when i spent 2 hours making a model of a room, and i imported it into unity. I came across some problems. The handle for the refridgerator was half gone, and some other knobs and buttons just flat out dissapeared and took some of the model with it. The little holes in the oven near the top used to have 4 knobs, now they are holes. And on the microwave, there used to be buttons. Now there is just 9 square little gaps. I went into blender (Yeah im using blender im 13 cant afford maya or anything), and used the triangulate modifier to triangulate the mesh but still no dice. How im i importing it wrong or did u just flat out made the model wrong?

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