[PLEASE READ] Crashing and Endless Loading

Introduction

Crashes and endless loading can have many causes and therefore usually need troubleshooting. There are a few known issues which can usually be found in the bug forum. Check the compiled list for any known issues.

To help you get faster help, please check the guide where best to post for your particular issues. It depends where in the game you have issues so posting in the right spot, speed up things.

For more information on crashing on, please check out this thread: [FAQ] Sims 4 Crashes (PC) (the thread is a bit dated but still valid in it's core) or Mac Crashing.

When troubleshooting your save, make sure you work on backups. Always keep an extra copy of your houses/Sims/.. safe somewhere.

Where to post

Depending on what you are seeing, it's best to ask for troubleshooting help before posting an bug report. Please use the forums below.

Crashing

First stop for crashing issues is the tech forum of your platform. Make sure to post your specs/state the console you are using.

Endless Loading

Please try to troubleshoot yourself first. If the tips below don't help, create a new in The Sims 4 Gameplay Questions & Issues

Provide as much info as you can, especially what you already tried and if you are a mod user.

If you have any files called LastException in your documents folder, please provide those when asking for help.

Troubleshooting

For crashing and endless loading it's very important to know WHEN the error occurs.

Game crashes/endlessly loads before main menu

Delete your Cache file. Also delete the scratch folder in your saves folder if there is one.
Remove all your mods and test without them. Details here: PC, Mac
Check the current Broken/Obsolete and Updated Sims 4 Mods thread in Game and Mod issues for known Mods/cc that crash the game.
Make sure your computer meets the minimum specs. Be aware that they increase if you are using lots of packs, mods/CC

Game crashes randomly

Usually best to create your own thread in the tech forum of your platform (see links above)

Game loads endlessly when trying to load a save game

Remove all your mods and test without them. Details here: PC, Mac
Check the current Broken/Obsolete and Updated Sims 4 Mods thread in Game and Mod issues for known Mods/cc that crash the game.
Use the load button instead of resume and see if the save loads this way. If it does, test other lots than your regular family to see if they load.
Please check this thread if it happens on all lots in a certain neighborhood: [PLEASE READ] Save Game Corruption | EA Forums - 5037272
If none of the families load, create your own thread for troubleshooting in game issues.
If it's a certain lot(s), see below.

Game crashes/endlessly loads reproducible when loading a certain household/lot

Remove all your mods and test without them. Details here: PC, Mac
Check the current Broken/Obsolete and Updated Sims 4 Mods thread in Game and Mod issues for known Mods/cc that crash the game.
Move out the family and test if you can visit the lot or enter in build mode when it's just the lot. Also test your family on a different lot/save
Sometimes the game throws lastExceptions while you trying to load. These give an indication on what's broken. Provide them when creating a thread.
If your game crashes when trying to load a certain unoccupied lot, especially in build mode and for buildings that worked before Patch 1.103.205/184. please use this thread: Endless Loading/Crashing when trying to load a certain lot
If your game crashes because of a certain family, please provide them in the gallery and create your own thread for troubleshooting in game issues.

The map doesn't load and stays a white screen

If it never worked and you are using T.O.O.L or other mods, make sure you have the newest version of those mods.
If it worked and stopped working after you placed a lot in that particular world, please use this thread: White Screen when loading world (Patch 1.109.207)

The game goes back to the map when trying to load a household

This behavior has multiple causes. You can read more info about it here: Loading a family just reloads the map. Most of the time you will get an error code but sometimes it just reloads the map. In most cases the game throws a LastException.

Search both the Bug forum and Game/Mod issues if your error code already has a thread. The first two parts of the error code are relevant (For example 102:a0adad34). If there's a thread, check for solutions and if you need further help, post there.
If you don't find a thread or you don't get an error code, create your own thread and post the LastException thrown (you can find the file in your documents folder. To upload create a rar file to upload or copy/paste the content in spoiler tags to your post).