I got a jangar arcanis stuck on impassable terrain because i accidentally pathed it onto it. Apparently you can path through it as well (tested it walking out of my shrine deployment zone). Potential global effects affecting this are Trailblaze. The map I was on was the Grove of Ashes.
It is consistant on different maps, and is related to having a Trailblaze unit out as far as i can tell, you can even get onto the art on the edges of the map off the grid, but you get stuck.
Knockback and Slam can push units into impassable terrain off the edge of the playable map, and lock them there forever...
