My game crashes whenever I choose a hat for my cc

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Instead of doing it, you could have checked the rules and shared blend files because we need to see what they looked like before you imported them in s4s. I get errors when I try to export them

Did you happen to edit the original blend file? The download links for the original are no longer available so I cannot check, but the problem lies in the fact that the mesh has all vertex groups of the rig in the list. The game really does not like it so that is why it crashes on you. I do not know why it did not crash on them, tho, it happens to everyone

Anyway, what you need to do is to delete all weights and re-do them because your meshgroups are rigged differently than theirs. This hair should not be affected by the head bone only. Check the last three tutorials by this person to know how to do this
Would be a good idea to re-do the uv_1 as well for their mesh is not affected by the right morphs

Well, let's just say that the item is not adapted the way it should be. There are too many vertex groups in the list, it is affected by only one bone, has no hat chops, and the uvs in the uv_1 are not right. However, I had no problem exporting the mesh, so there must be more to it than just too many vertex groups ( or perhaps it is related to the version of the game / s4s the item was made in,  i don't think I've ever had any problems exporting the mesh, but we don't do that often in the first place, so who knows )

There are videos on youtube, search for "the sims 4 hat chops"

 Everything works fine for me when I fix it.
When you duplicate the mesh, vertex groups are not affected.
You need to duplicate the mesh twice to create 2 hat chops for 2 types of hats.

- delete empty meshgroups;
- select the remaining one, delete all vertex groups;
- click on + to create a new vertex group, name it b__Head__, select all of the mesh with A, assign it to this vertex group;
- add a new vertex group named b__Spine2__, select it, switch to Weight paint, disable Limit selection to visible, choose Weight gradient, click and drag it like in the pic;
- click on Normalize all;
- duplicate the mesh and make hat chops, change cut numbers

Clone a maxis base game hair and import meshes and textures there. The bones have already been added to a package, so must be that

Try this, it does not crush the game for me. If it works for you, then you did something wrong ( did you delete all vertex groups before re-assigning them? )