Thanks for the replies, David Kastrup, Thomas Morley, David Nalesnik. The problem is fixed, and if you care to read how, keep reading; otherwise, thanks again and have a nice day.
While trying to figure out how to create a "tiny example" that would duplicate my problem, which I was sure had to be happening because of the complicated layout, score block, incipit and choir staff markup etc etc, I found the problem, and it was very simple.
When I was preparing this score with version 2.18 (from an original file that was in version 1.4), I had left the bass lyrics block with
textobassus=\lyrics{ rather than
textobassus=\lyricmode{
This was close enough that it compiled all right, and Frescobaldi did not flag it as an error, but it was enough to create the two little problems I mentioned originally....both are fixed now.
And it took me less than 6 hrs.
Thanks again.