Today, when I tried to open my game, everything went well, until the menu loading screen reached a specific point (When the title says "Redistributing Resources...") then it stopped responding completely, and I had to restart my whole PC to close the game.
I tried again, but the same thing happened. Then I thought that it might just be an issue with cache, and I deleted the groups.cache file but nothing changed.
Yesterday it was playing fine. I don't really know what happened now.
It's always at that specific point then it freezes, at the Redistributing Resources title. It doesn't crash, just freezes and never gets unstuck.
I've also noticed that the game takes way longer than it used to to load completely.
What is going on and how can I fix this?

Have you added any new CC/mods to your game lately, or shifted any of it around (loading order, etc.), or done any other changes to the game files or otherwise? If so, it's likely something is making the game stop loading at that point.

Test without CC/mods, if the game loads fine, it's CC/mod-related. If you know what you've added since hte issues started, start with moving out those items, and see if the problem resolves. If not, check with the usual tools - HCDU+, 50/50, etc. until you find the culprit.

Other changes can potentially have caused it too - updates, moving files around, OneDrive, what have you... Basically, anything that's different since the last time the game loaded fine.

Try deleting "Accessory.cache" too, if you haven't already.

I hadn't really changed anything or added any new CC to my game, I simply just opened it and then it happened. I'll still check if there are any mod conflicts, though.
In the period of time where I hadn't opened my game before it happened, I didn't do anything with my PC either, which I had thought of it being the cause.
You're right about accessory.cache, I had only deleted the "groups" one.
Thank you for your help!