I was able to lunge below the world in Forlorn Streets, screenshot below.
Sorry about this! What was the target that you used lunge on? Was there something below the bridge, or did you hit something on the bridge and were forced down?
I had this happen while leveling my new Sentinel Yesterday morning. Happen to me in Citadel Sewers when i Lunged into some breakable Boxes. I tried to place a portal and could see it on my minimap but couldnt move or enter it so i was left with no choice but to exit the game and log back in.