Edit: This is likely a duplicate, being a different incarnation of this bug:
In Alpha 3, a worker keeps getting stuck on scaffolding. It is always the same worker, but not always on the same piece of scaffolding. This causes the worker to ‘spaz’ quite a bit and the CPU usage maxes out (light yellow is the main color on the CPU usage meter). After this, even if the worker becomes un-stuck, progress on building and farming by all workers grind to a halt. All the workers pick berries, eat, sleep, then just stand around all day. Even the pet raccoon stops eating… Also, this ‘problem’ worker seems to get stuck again doing many other tasks such as eating, grabbing a log, picking berries, etc.
I am not sure if the worker getting stuck is causing work for everyone to stop, or if this is just a coincidence that both are happening together (save/load bug?). Two save files are linked below, the first being right before this bug happens, the second after the worker has gotten stuck/unstuck several times (causing an unfortunate beheading…)
Hope this helps.