I recently found that I can make sub assemblies from existing assemblies.  But I have also found that I now have a few cases where in the top most assembly, one of the next level down [usually the first one] shows a rebuild indicator [the traffic light thing] in the feature tree.   Talking to the local support  guy, it may be a circular mate reference or something like that.  But how do I find that?  I've looked through the features, and mates, Some seemed to be in an odd order, so I arranged them to be in the order I added them, at least as much as I can remember.    But is there now way to trace down where the problem is coming from?

I even had one that fixed yesterday, but today, I opened the file, and the rebuild thing is back.