This is the code from the EPUB:
And here's the AZW3:
@jhowell
These problems with the AZW3 don't show up when viewing the file with the Calibre viewer. They only show up when loading it onto my Kindle or viewing the file with the Kindle Previewer app.
@Mikou
It seems to be extra spaces, as best I can tell. Because sometimes the size of the gaps that are inserted is different on different lines.
In the Calibre conversion options, I basically unchecked absolutely everything I could, so it would be as direct a transfer as possible. However, I have since tried checking certain options that might conceivably have an effect on this, and seeing if it makes a difference but it so far hasn't.