See that is the issue. You reinstalled the game, but kept the mods. Also, sadly NMM is one of those, at this point, archaic mod managers that directly installs mods into Skyrim's real Data folder and not subfolders for each separate mod making them isolated from one another. The best analogy I can give is that with more modern Mod managers your mods are packed into small boxes that are placed one next to another, you remove one but nothing happens to the others; while NMM on the other hand is chucking everything into one big box and you don't know what mixed with what in there during the stuffing process. So if it does overwrite something or change something it is next to impossible to figure out what and why. Might be time to switch to some of the more modern ones like MO2 or Vortex. Or, if you are dead set on NMM, look it up on github since people are still updating it there.
Also I am genuinely surprised you got a 2k mod setup working for as long as you did, but when you reach those numbers breaking your game is an inevitability. As a rule of thumb don't overload your game with script mods (quests, perk overhauls etc.) and for the love of all that is Holy never turn them off and then load a save file where they were active. That is one of the easiest ways to brick the save. If not immediately, then inadvertently by some other mod.
Best advice, start clean. It hurts like hell (I had to do it not too long ago), and many mods might not exist anymore, but it will guarantee a stable and working game. And since I am already delving into giving my personal opinion I will leave this message with this last piece of advice. Might wanna cut down on the mods, 2k is really excessive even if 50% of them are not houses, armor or weapons.
But thank you for the information! I was wondering why i didn't find anything ^^
