Short way, AI stopped doing anything, no one moved or did anything, even though building kept still doing their things. Everyone literally stopped, and kept doing their animation, but still standing still. I could move them, but if i would do it they would just stand there and keep doing animation they were doing before i moved them. This happened after night came cycle 90 and i just went off priority screen. After that i reloaded my game. After reload, everyone started to do job that was near to them, not with priority, just nearest. Which meant everyone started mobbing. Then I went to main menu, loaded game from there and everything went back to normal.
Reason seems to be perfect timing with priority order and night coming, i include few pictures of my priority screen if they could help, even though they were after i fixed it. Panicked and did not take pictures immediately. They were doing hydrogen piping in top when this happened. Hope this helps (:
I will also include my log file, it tryed to reproduce happening from cycle 89 two times but i could not do it.
Make complex priority commands and make them happen same time when they are meant to go to sleep. It seems like it mixes AI commands and it will cause loop inside code that wont let it leave the job they are doing.