I am trying to find a solution with some imported geometry from another software. I attach the files of the assy and the parts. As you can see I have done a symmetry but there I cannot find a way to make the resulting parts to be visible and there is no error message whatsoever from Solid Edge.
From looking at the part files themselves, I notice they have all come into Solid Edge as construction [surfaces].....there are ways to fix this, both on the existing files, but probably more importantly, for other files like this.
Or, if you simply just want to show what you have done there, in assembly, you can right click on each of the mirrored parts, and choose "Show/Hide Component", & check the "Surfaces" "On" box. [warning...constructions being surface sets only, they have no actual volume....until they are converted to solid models]
What neutral format are you using to export from your other software?.....also, when importing that format into SE, check the "Options" available, prior to selecting "Open".