In order to gather from a resource, villagers need to go to a free spot next to the resource. If they can't find or reach a free spot, they'll look nearby for another resource of the same type and gather from there instead.
In the case of hunting, that means your villager will proceed to kill their next prey and gather from it.
This can happen for multiple reasons:
- The animal wandered too close to a building, a cliff, another resource (tree, deposit, etc.) or the edge of the map before it died. This reduces the number of open spots to gather from, since villagers can't move where there's an obstacle.
- There are too many villagers gathering from the animal, so there's no free spot left next to the carcass.
- While moving to gather, the villager's path was blocked (e.g. by another villager moving towards the animal) and couldn't find an alternative path to an open gathering spot.
Unfortunately, there's very little you can do to prevent this, other than careful micromanagement.