I don’t have Sweet Home 3D so I can’t tell how much of this problem is on that side but I can see several issues in your model that may or may not be a factor. the first, glaring issue is the exposed reversed faces. If you look at the model in Monochrome face style, those reversed faces will be evident because they’ll be displayed as blue instead of white. You can see some of those reversed faces in this screen shot. there’s also a great deal of unneeded edges. cleaning them up may help with your export.
The other glaring problem is the incorrect usage of layers. You have some faces and edges assigned to the “details” layer. Edges and faces should always remain on Layer 0 (also keep Layer 0 active at all times) and assign only components and groups to layers other than Layer 0.
This is the result of turning off the details layer.
Except for the components which appear to be imported from the warehouse, the rest of your model is all one lump of geometry. this makes it difficult to work on. You should be making components and/or groups of discrete parts of the model.
And your model is drawn about half below the red/green plane which is the ground plane. With shadows turned on you can see that.
