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So when I download the file and bring it into Cura it shows up fine, Cura just needs to scale it 100000% (not a typo) for some reason giving the left part dimensions of 135x125x33.
I think I know what is going on. I use Creo Parametric for my design work as it is a program that I know. Creo is working in meters. My guess is that when I export the file to an STL, its dropping the units and seeing a dimension of 0.135x0.125x0.033. This is extremely small and is most likely why you don't see anything on the build area. Let me see if I can recreate them at the appropriate size. If you don't want to wait, you should be able to scale it up.