Mods
What have you done within the mods folder? So many things can happen here. We will examine what can go wrong with various types of addons and replaces.
First let's talk about quantity. Too many mods installed, particularly high polygon count vehicles or massive maps and MLOs. GTA5 was not designed for modding. Push too far, too much and you will crash no matter how powerful you PC and your GPU specifically.
You can mitigate issues with properly configured gameconfig, visual settings, and the proper hardware but at some point too many mods and the game will cry Enough! and crash.
Secondly, let's talk about currency or recency. By that we mean, are the mods updated? Outdated mods can be defective mods, they may no longer work with new versions of GTA 5. Old mods do die.
There are so many things that can go wrong inside the mods folder. It could be addons, replaces, or customizations to the meta data files, as we shall see in the next section.
Peds have their own issues because they require proper entries in the peds.meta file - whether they are normal or streaming, male or female, etc.
Remember that your mods, addons and replaces, aren't the only DLC. The game DLC, particularly after a patch or update may conflict with installed addons. Removing the new DLC from dlclist.xml is often a quick way to test for these potential conflicts.
So in summary troubleshooting mods, due to the complexity and variability, entails renaming the mods folder and testing to see if the game runs or not. That's the surest way to rule out issues with mods if your game doesn't load or crashes quickly or randomly.
Prevention is key: An ounce of prevention is worth a pound of cure. This means not installing too many mods, following instructions, installing mods one by one and then testing, care with editing configuration and meta data files, and backups. Backups are so important.