I realized that some villagers randomly steal workstation of other villagers. It happens when more than two villagers have acces to a workstation, and maybe when it's time to work for villagers. I provided two screenshots that shows the issue, in the first one there is a lonely and employed villager into a small area and also there are more villagers next of him into a bigger area, but they are unemployed. The second screenshot shows that after few minutes, the employed villager became unemployed and the employment was taken by a nearby villager that also have acces to the workstation.

Also I observed that maybe there is the posibility that the villager itselft leaves the workstation randomly, so all of those problems could make very difficult trading sistems with villagers.