"Reload from Disk" With STL Split into Objects?

A couple of days ago, I made a first prototype for an insert into my car to prevent my phone from sliding around. The color won’t be green in the end, I was just using that filament for my test pieces.

I exported a STEP file from Fusion 360 and this is one side that was rendered properly in Orca and Bambu Studio, it has a fillet in the top edge:

This a different side was rendered in the slicer, it was the same height, but a little wider and had the same fillet, part of it was ok, but the rest looked like this:

I then exported an STL file from Fusion 360 instead and it rendered properly.