For some reason, this white rectangle appears and blocks movement on the staircase. Location is Ivy Tunnel Control Point, in the West (I think its Constitution Hall) but this was kind of a strange anomaly that appeared in game.
Same in my game.
Was going to post about this. But i found the same issue.
And just visible from the position you are if you approach from up you cant see the white box at all and something invisible is blocking you.
It's been reported a few times.