Ever since I reinstalled Skyrim, I've been having this problem. At seemingly random places in dungeons, I'll collide with some invisible barrier where normally you'd just walk on by. I only notice them along bottlenecks, such as hallways or stairs, but they could also be there in big rooms and I just haven't seen any. This only happens in dungeons, never in cities or houses or out in the wildnerness.

The effect is effectively complete blockage. I collide with it, my followers collide with it, and so do the draugr or whatever else happens to live down there. They can't be jumped over. Arrows and spells bounce off of them. I've looked all around where these barriers are and there isn't any indication that anything is wrong.

Sometimes if you hop and strafe back and forth along its edge long enough, you can pass through. Other times you slip outside the map and start that long fall into grey.

I'm using a handful of mods, but these are the same mods I was using on the previous installation where I had no problems. Besides, as far as I can tell, none of them make any changes to dungeon maps.

Any idea what might be causing this or how to fix it?

I've recently noticed the same thing. Are you by any chance using enhanced lighting and FX?

I've noticed some collision problems with this mod in the past.

As Fragonard said - there's a new version of the mod due soon that should address these problems.

Yep, I'm using that mod. I'll disable it and report back if the problem persists.

Thanks a bunch.