I have encountered a situation where a worker located above stairs cant reach his works storage area when it is located below the stairs. If the stairs are removed, pathfinding works again.
When the worker is located below the stairs, he places goods in the storage area and immediately takes them out again. in an infinite loop, until the stairs are removed.
The exact same staircase situation can often be found in the village, but the bug only occurs in one place, which is why I am uploading the savegame data.