There were no error messages at all, but then I found something when I went to "Clean" up the Android packaging project. It seems RenPy couldn't find some images to clean up, but they were clearly included in the package. The issue may have been that for images, I use a lot of nested folders and the directory tree can get quite deep. I note that with some programs, once a directory address gets long enough, programs can no longer understand and find them.
So I cut the image directory tree in half and made it more shallow, having a Pt 1 and Pt 2 of the images. That seems to have worked.
We'll see when I try and make the next build if that was the issue.