Ed (& everyone else),
That may be it... I have the "Major Assembly" made of some "Sub-Assemblies", and then the hardware (from the toolbox), and a few brackets, etc., to hold it together - i.e. like you would build it in reality.
I had a "width mate" (which can be handy at times) especially in this case since these "panels" that get installed are movable, then you drill and rivet on site. Anyway, once I got ride of that width mate things cleared up...almost.
I did notice something strange (and I will mention an "artifact" later), I had a part that seemed to have been mated to itself??? I do not know how it happened - you cannot do it, SW won't let you - but it was an edge mated to a nearby radius on the same part - a sheetmetal part. After I deleted that mate, the part changed orientation and all was well again, and the assembly is living happily (it loads faster) ever after!
Now for that artifact I mentioned earlier... a few parts in these assemblies in question kept loosing their leaders of notes on the drawing sheets. I always check the PDFs I send via email and twice I have had to go back into the drawing and re-enable the leaders! I noticed this when I control-c copied a note from one page to another in the same drawing, then saved the drawing in PDF format. Under review of the pending/to-be-sent email, I saw the problem... just thought I would mention this for added confusion :^}
All seems quiet in the land of oz for the moment - I've made it to "Munchkin Land"... all parts, assemblies, and drawings are working, and the "Lollipop League" is happy. See: