So just wanted to led the devs know:

I was playign through the level 'Yesterday's News". Got through the Tube station, and took a detour tot he right, as I guessed there'd be a collectible there. I was right. After a bunch of tries, I managed to jump-dash onto the roof of the shacks there, and found myself stuck with no way to get back to the playing area. I also spotted the question mark, locked in a small room.
Anyway, as I was looking for a way out, I walked inside some dark corridor, and suddenly I was falling through the level geometry, as the city receded above me, and my objective marker started adding more and more distance . (I let it go to 3000 m before restarting from a checkpoint)

This should probably be patched out. [s] And does anyone know how to get that damn collectable? [/s] lol

EDIT: nvm about the questionmark, I missed an open doorway. (fat rat BBQ), lol