if often related to a pathlenght bug in mq2nav, a fix is coming for it in kiss once maskoi redoes the pull sub.
but basically as eqtrader74 said, at some point the pullpathlength becomes long, and then mq2nav bugs out, and just creates the shortest path it can to your mob, and that is often through a wall or over a mountain it cant go.
the fix is basically checking the pathlenght against the distance of the mob, and if its smaller, since mq2nav only counts the bit after it warped past the wall or mountain, its a bugged path.