You’re right, of course.
It’s just that I wasn’t expecting the first rebuild to fail, so that caught me off guard.
The message was there, but I because it was in the wall of log text, I lacked confidence that I would find whatever the problem was. For all I knew it was going to be some obscure exception buried in a call stack. Once AI told me, I saw it was right there near the bottom.
I guess this is what happens when one is a part-part time webmaster 