Skyrim Open Cities Mod
Before displaying the load order, add-on mods such as Frostfall must be loaded under their root mod on the screen (Campfire: Complete Camping System). Frostfall will load later of course, but for it to work, it’s dependent root mod Campfire must be first (higher on the list) and since it must remain above everything, this.
Not sure if this is your mod, because I have around 20 installed, but yours seemed the most relevant to this so I figured it must be yours. In all of my games when you enter Solitude and turn directly right there is a rock that you can 'open' to 'enter Solitude'.
Skyrim Open Cities Mod Download
Skyrim Open Cities Mod List
When you open it it brings you to an alternate version of Solitude with no people and doors that play the opening animation when you touch them but don't load a new place. The only way out is to enter the rock again. Not sure if this is yours but wtf.