Hi!
Could be a few things.
1: The hinges need to be replaced. Now you stated that they are fine, if this is the case, then make sure that they are all the way in.
2: It's related to the shell. It could be like millimeters difference from your old shell, but could cause problems with the hinges... It's really difficult to see with the eye, but could be really a thing... If this is the case, you could use your old shell and if this is fine, then it's like 99% your new shell which need to be replaced.