I recieve a lot of assemblies a step files, and for the most part it works fine. I drag and drop the file into SW2018 and when it opens save it as an assembly, which converts all of the included components to parts. However, I just opened a step assembly which did not save any of the components as parts, and the feature tree looks like this:

I can't open or save any of the parts, or move anything. Any idea what changed, and how I can fix it?