Found a bug were the enemy AI turn could get stuck if the pathfinding totally failed. ːnotsohappychappyː
Looking at my code comments it seems I had tried to fix this 10-12 years ago ... but had not added an emergency fallback. Now there is a fallback, if the AI path to it's selected destination completely fails and cannot recover, the AI will get a random path target. ːcorblimeyguvnorː