It seems that you've hit one nail on the head as far as a bad book goes. I haven't searched for it yet, but I did notice a discrepancy between the number of books selected in Calibre, and the number that were actually on my Kobo.
For the latest round of tests, I reduced the number of books to 45, and they all got sent to the Glo. After the Glo had processed them, re-connecting and disconnecting did not result in another "Processing Content" screen.
Unfortunately, neither did it result in the series data being displayed. Calibre finds all of the books on the device without trouble, but none of the series data seems to end up on the Glo.
I have created a debug log as you described, and have sent it to you in a PM. Hopefully you can make some sense of it.
Thanks for all your help on this.