with R27 what appears to be a new bug has started where after almost finishing a room the workers will take some wood to the stockpile and then just stand there doing nothing until they get tired enough to go to sleep. but even after they will not resume any task new or old but there animation cycles reset at least.
edit: after they have slept they will start to respond to new tasks for a short duration but will freeze again. also somehow this will also freeze the carpenter who is not doing anything related to the room.
edit 2: looks like a second stockpile will partially unfreeze the AI