Importing a 3d model, textures wont show and a grey object appears when I rotate the model too far

As the title says, I’m importing a 3d model plane a client has made into a file I have set up for a shot. The shot has a background and a camera I set up in it. I tested the model in a new file and still the textures didn’t show, but the grey object didn’t appear. The grey material only seems to follow the wings and when I rotate the plane too far.