When AI move from outside onto a building path, they always choose to start walking. Walking improves the precision of their movement, and their manoeuvrability.
AI can sometimes overshoot this transition to walking and run into/through building geometry. This leads to AI clipping through walls, floors etc.
Presumably this takes place with the AI unit run animation starts just before the AI decides to start walking.
If AI are moving into a building, they should start walking before they reach the building, rather than as they reach it. This would reduce frequency of AI clipping through walls, floors, etc.