please tell more: did you use PROJECT2 command for the 2D display, or you scripted an independent 2D symbol? Are you using binary 2D, or scripted? What does “add to a new pln file mean”? You load the object with library manager, or copy paste it from another file, etc. Best would be if you could send us the object in e-mail so we could take a look, or if you want more people looking into the matter here on the forum, upload the object to this forum thread.
Your object is calling another object called “stages 45” in the 3D script.
I would be guessing this is in the embedded library of your original file which is why it works there but is not loaded in any new file which is why you are not seeing any 3D.
You need to export that object from the original embedded library and place it in your loaded library.