The linked video is evidence of pathing issues in Velketor's Labyrinth near the Frenzied Velium Broodling spawn point. Mobs that are pursuing players to the east of the spawn point may clip over the vertex of the walkway at location +391.1, +42.7, +36.7 and drop down to the lower levels of the area, causing trains as they then climb the walkways back to the player.
2019 12 16 Pathing Issue at Frenzied Velium Broodling spawn in Velketor's Labyrinth