Could you please try copying images from your hard drive to your desktop & then try importing them into Lightroom while all external drives are unplugged?
I copied 180 photos from iPhone #2 to a new folder on my desktop called "Copy of iPhone #2". I did this using Image Capture (which is a standard app on mac desktop computers)
I imported (using Copy, not Add) all 180 photos from folder "Copy of iPhone #2" to a different folder on my desktop call "Import Test"
Success. Lr did not crash and all photos were imported and copied to the Import Test folder.
That seems helpful, now what?
My suggestion would be every time you want to import images from 1 hard drive, keep the other drives disconnected.
I am importing from an iPhone. I tried disconnecting all external drives. It fails.
Image Capture can move images from the iPhone to the internal drive. Why can't Lightroom?
In my original post I stated this:
Disconeect all external drives, import to internal SSD : import fails
I updated to Sierra 10.12.1 today (Oct 24th) and import started working again. I successfully imported 369 files (over 1Gb) of photos/videos/PNG from iPhone to Sony 1TB 5400RPM External HDD connected via FireWire 800.
Solution: Sierra 10.12.1 works. Sierra 10.12 did not work.