What does the green arrow mean when added to the feature tree symbol for a part or assembly? I couldn't find it in the help topic which identifies feature tree symbols.

I suspect it indicates the part or assembly is embedded in the main assembly, and I would like some words to help me search out that topic.

The long story:

I am trying to import into SW2018 a step file that came from a customer's SolidWorks assembly. The parts appear nicely on my screen after the import, but when I save the file, I get 10 error messages saying "the part was not successfully saved". If I try to open the saved SLDASM file, there are a number of parts missing and a lot of errors. From the import, I am unable to open the individual assembles or parts that make up this assembly. Is there a way to regain a usable structure? I assume there are some minor import errors for a few individual parts in the assembly. If I could repair or suppress those, the rest would appear correctly.