This has happened to me several times lately. I build a mill near deer but the workers do not start killing the deer after they have build the mill. Instead they just stand there idle. Even if I kill some deer, the do not start gathering from the deer.
Similar thing when I do boar hunting. I build the mill, kill the boar, and the workers are just idle instead of gathering the meat from the boar. I then have to order them manually to gather from the boar.
I know this worked correctly some months ago so I guess one of the recent patches introduced this bug.