It sounds like you have OneDrive on your computer. That's a cloud-based storage that is included with Microsoft OS's like Windows 10 and 11. It has a bad habit of "fixing" your content by taking what it has saved in the OneDrive cloud and "synching" it so that it removes what you've carefully fixed in your mods folder. Then all sorts of problems happen (such as outdated mods causing corruption.)
Unfortunately, TS4 is too easy to corrupt, even without mods. But outdated mods definitely can cause it. This really complicates how EA can troubleshoot what is wrong with someone's game, since the corruption may not show up until you've been playing a while (even if you took out the outdated mods which put in the "seeds" of corruption.)