In preparation for Skyrim Anniversary Edition, and the modpocalypse expected to follow its release, I trimmed my mod load down to a respectable handful. Essentials like Alternate Start - Live Another Life and some additional followers, including Inigo and Lucien. I started a new game and everything was fine, until I quit to do some actual work and then tried to reload that game on my lunch break. A black screen, with the music still playing, was all I got.
None of the usual Skyrim tricks—switching to fullscreen borderless mode, running it as an administrator with Windows 7 compatibility on—seemed to help, and then I found a post from modder Joseph Russell, the creator of Lucien, who has figured what's causing out the issue. Turns out other players are having the same crash, which is caused by the latest build of Skyrim running scripts faster than previous ones did. This causes problems with mods, like Russell's, that rely on them.
Whether you bought the Anniversary Edition or not, your version of Skyrim Special Edition has automatically updated to one built with a new compiler, Visual Studio 2019 rather than Visual Studio 2015. And that seems to have made it slightly too efficient for its own good.
As Russell explains, the problem "was coming from my patchless interaction system, which checks the player's mods when they load the game and fills aliases with NPCs from other mods, such as Inigo." The script for that system, which searches for esp files—mods with plugins that add or modify world content—was running faster than it used to. "This meant that when the player loaded the game, Inigo's esp was detected," Russell explained, "so the game tried to grab his reference to put into the alias. However, as the script was running so fast, Inigo's reference hadn't had time to load, so the script was attempting to fill the alias with a NULL, causing a crash."
Russell fixed it with an update to his mod that adds a three-second delay to the script, though if you're having the same problem—which even players on Xbox are experiencing—it may be caused by other heavily scripted mods. I've disabled ones that add followers for now, and everything's working fine again. For now.