Turns out the bishop is in the colony, but due to having lost the profession, it can't change profession from the domestic advisor and it's hidden in the colony screen, meaning it can't change profession there either. No idea how this happened, but the same can happen (rarely) if a fisherman is removed from a plot because of a pirate. I made a fix, which once every turn will look through all citizens and then kick out those without professions. This way when a unit vanishes, it will end up on the colony plot on the map the next time you click end turn. That's the best I can do without knowing what triggered this condition. The good news is that this fix will work on existing savegames. The bad news is that autoplaying triggers this once in a while, meaning there is an underlying problem, which has yet to be found. More investigating is needed, but at least units will not get stuck in an idle and unreachable condition. I'm aiming towards a new pre-release, but I need to fix a few things first. Hopefully it can be tomorrow. Sure. The savegame format doesn't look like it is to blame for this. Not sure about learning by doing either. I highly suspect this to be an old bug, which people either haven't noticed because the units are hidden from the colony screen or that it's really hard to trigger. For all we know it's the first time ever that it triggered on an important unit like a bishop. People would care less for a missing free colonist.