Pets in Blackburrow
 

My last three pets have straight fallen through to the second floor of Blackburrow causing a massive train. Now I am aware of the bad pathing, but is that the issue here?

Summoning a pet while too close to a solid object sometimes makes the pet spawn inside the solid object and drop, but I've never heard of pets just falling through floors unless you're summoning them too close to a wall or similar.