Warehouse - Poseidon Reservoir - Doorway blocked by invisible wall - Why?

[Rostagar]

There is a warehouse next to Poseidon Reservoir that has an open doorway that can't be entered despite the player having plenty of clearance. The doorway is located in the side area of the warehouse (where a desk and some stairs are). I've looked inside Creation Kit to find the reason why and can't seem to find it. There is a large acoustical zone that fills that area (with a black line running through the doorway) but that shouldn't be the reason since you can run through that zone elsewhere without being impeded. I'm pretty certain that I don't have a mod installed that would interfere with the doorway. Has anyone else encountered this bug and understand the reason why the doorway is mysteriously blocked? Thanks.