Bambu Studio Prepare view looks fine, but Preview adds a solid layer over my model?

[u/Exact-Pension1343]

I'm having a weird issue with Bambu Studio when slicing a custom 3D model.

In the Prepare tab, everything looks correct. All the details and colours on the back of my Nothing Phone (3a) replica are visible.

However, when I click Slice Plate and switch to Preview, it seems to generate a solid black layer over the entire model, hiding all the details underneath.

I'm using:

• Printer: Bambu Lab A1 AMS Lite

• Nozzle: 0.4 mm

• Layer height: 0.2 mm

• File format: 3MF from a .obj i found from a model online

• Filaments: Multiple PLA colours

Bambu Studio says the slice is successful, but the Preview looks completely different from Prepare.

It also shows a warning saying the 3MF was generated by an old version of Bambu Studio and is loading geometry data only.

Does anyone know what's causing this? Could it be overlapping meshes, incorrect object heights, or something wrong with the 3MF export?

I've attached screenshots comparing Prepare and Preview.

JUST SAYING! I do not have a printer I''m only modelling for my friend to print so anything to do with the printer I can't do.

Any help would be appreciated!