The space between filament pockets was a little too small.  It failed to render to greater than a single nozzle_width at the base of each pocket, so the wall between them disappeared on slicing.

Tweaked the model a little.  New files are up.

Then I got to battle a new issue.  One of the magballs on my printer unscrewed itself a little and was driving me mad.  First time in about 3 years, so I guess I was due for it.

Printing again.