Kelnin's dome can push players through the map.

[Armroker]

Essentially, when the expanding dome pushes the player and if the player hits a wall or other surface, there is a high chance that the dome will push the player through that surface. In the clip, Talon hits a pillar, and the game pushes him under the map. Casting Dome directly above the player's head will push them down under the map.

 

[bdesroch]

Something similar happened to me near mid, kelvin used his dome and I fell through the map only to be stuck under mid without being able to use unstuck, effectively losing us the game as my team was playing 5V6.
Match ID: 44834862

 

[PKPenguin]

Happens to me all the time as Warden, not sure what causes it.