After an update/upgrade, noticed certain daemons not working. Investigated past the obstacle that is systemctl<spit> to find that (for example) transmission-daemon wasn't ship-shape. So, purge and reinstall. Still not working. aptitide whining that dpkg could not find the pi:pi user:group. That has of course been unused and long removed (at install time, normally) and proper user accounts and passwords set up. Temporarily recreating it allowed me to install trans.-dea. Then to install git.. Same problem. Same, somewhat unsatisfactory, "solution".
What a /bizzare/ thing. :-/
Ok.. Who broke it?