Cloth testing, bad result

Ok, I've gone back a few steps. Do the basics, left the texturing.
Still a mess.

prnt.sc/26ex332

File: drive.google.com/file/d/1ItbkPanrGeR0Y1yrz_u-k9o04gWxeMcb/view?usp=sharing

you need to make sure everything works fine before doing things that would have to be undone if everything is not fine. You need to make sure the mesh morphs, moves, displays textures right before splitting it into meshgroups because, if it does not function right, you will have to join it again, re-do weights/uvs, then split again.

You also need to have a rig with all body parts in the scene and only two uv maps. The second uv map is responsible for morphing. There are places on the mesh that are not rigged at all.

Step away from this project for a second, otherwise you're just making it harder for yourself to learn the basics

Make a quick garment:
- clone a bra, export, open the blend;
- in edit mode select everything with A, remove doubles with merge distance set to 0,0001, Mesh - Faces - Tris to quads, enable Compare uvs;
- enable sync and delete arms, neck, and a bit of the belly to create a quick top;
- Uvs - Seams from Islands;
- split the big island by selecting an edge loop and marking it as seam;
- in 3d view select the remaining top, press Alt S, type, 0,02 to offset it a bit;
- you can leave the uv_0 as is ( if you do not want to practice this) or you can unwrap it and move the uvs out of the uv space;
- delete uv_1, weights, vertex paint with white;
- rename this to Garment.

Now you have the type of mesh you'd get straight out of MD.

Prepare the reference/body:
- since this garment does not go below the navel, we can just use the top under the rig. Unfold the rig, make the top selectable and visible;
- select the top, in 3d view press Shift D to duplicate, Esc to confirm;
- press Alt P and choose Clear and Keep transformation to unparent;
- rename to Reference;
- hide the top under the rig.

Adapt it:
- select the reference, shift select the garment, switch to weight paint, choose Transfer weights, set the rest like in the pic. Then use Clean with All groups and Limit total with 4;

- select the garment, add a second uv maps, name it uv_1. Add data transfer modifier, choose the reference as source object, set the rest like in the pic;

- vertex paint the garment with 00ff00;

- select the reference, disable Limit selection to visible, select everything that is covered by the garment, delete it. Select everything and remove doubles. Select - Select boundary loops, mark them as seams;

- join the garment with the body. Alt click to select loops in places where the body is meat to connect to the garment, press the space bar and type Bridge, choose bridge loops. Do not worry about the uvs for now. Do this in all other places the body is meant to connect with the garment. Note that, when you create geometry like this, the seams do not continue, so you should mark them manually

- now, in uv editor switch to vertex select, press B, select the garment's uvs, press Unwrap again. If you were working with uvs that were not created in blender and wanted to preserve that shape, instead of unwrapping, Select - Less, switch to Face select, Pin. Then select the uvs again and unwrap;
- select everything and set the background ( the skin or the template), the uvs of the garment will stretch, so bring them back to the original size with S Y 0.5;
- with both uv islands selected, start scaling them down until the biggest fits where it needs to be. Then you can deselect the biggest one and place another next to it. If the uvs must share the same texture/pattern, they must never be scaled individually. Also, never rotate uvs freely, only by 90/180/270 degrees. Individual scaling or free rotation will create difference in quality of the baked texture and applied patterns;

- with the garment's uvs selected, export the layout as png, adjust the opacity to be 1. This will be your temporary diffuse;
- so if you will look at your item in the solid shading, you will see the dark shadows around sharp edges. Enable sync again, select the garments uvs. Shift H to isolate the selection. Select boundary loops, Select - Select more/less- more. Shift H again. Select boundary loops again. Mark them as sharp. Unhide everything with Alt H. Select one sharp edge marked as blue, Select - Select similar - Sharpness to select the rest, Mesh - Edges - Edge split to split;
- assign the type (geom) and the cut number (0000), save;
- open the cloned bra package, import the blend and the exported layout as diffuse. Temporary you can make other maps blank;
- check how the mesh behaves in CAS. Change the breast size, body mass sliders, play walking animation.

How to know if your item needs to be split into meshgroups:
- while in CAS, put a choker, a necklace, an armband, bracelets, tall boots ( if making the bottoms/full-body outfit). All of these items must be from maxis, no custom ones. If any of these accessories clip into your garment, said accessory needs to be hidden.
- let's say, you want to hide the shadow the necklaces cast on the body. Clone yfTop_VestLeatherStudsTank, export the blend;
- you will see two meshgroups: in the chest area ( tuned to hide the shadow ) and the rest of the top. If there were many of them, id suggest you to rename them to r(eference)+(the last digit of the cut number), so r_0, r_2, r_3, etc. This is the only thing that matters so that you don't mix up the cut numbers. But in this case you can simply delete the meshgroup that is the rest of the top and leave only the chest one;
- File - Append, choose the blend with the garment that you made, then Object, then the meshgroup with the garment. Append from Library. Delete bone_bone_shape.001 and rig.001;
- select the appended garment, optionally switch how it is shaded or the shading of the whole scene, in edit mode select the area that matches the chest meshgroup. You can switch the shading back. P - Selection to separate;
- select the separated meshgroup and give it a cut number that corresponds to the original chest meshgroup. In this case, it is 0000, so the other meshgroup should have 0001.
- download this addon ( enter 0 and click on purchase, in Blender go to File - user preference, switch to addons, choose install from file, choose this file), remove unused vertex groups from all meshgroups;

- delete the reference, save, import the blend in the yfTop_VestLeatherStudsTank.
- check how the mesh works in CAS;
- now you can go back to the pre-split blend file and bake textures;
- make lods, check how the mesh behaves on the lowest settings in live mode;
- upload thumbnails if needed.

I think I’ve mentioned it before but the mesh must have no gaps before you transfer weights. You do not need to retransfer them but you need to remove doubles.

S4s check the names of uv maps for objects only, but overall the order determines this, not the names.

You can see for yourself by rotating this image in the image editing software.
previews.123rf.com/images/garrykillian/garrykillian1704/garrykillian170404416/76337438-vector-damask-seamless-pattern-background-classical-luxury-old-fashioned-damask-ornament-royal-victo.jpg

You need to clone a different item first, made of one meshgroup. Like I did in the tutorial.

You removed doubles the wrong way then:
- join all parts of the mesh;
- in edit mode Select - Select boundary loops, mark as sharp. This will make you remember where they are;
- select the whole mesh with A;
- Remove doubles with Merge distance set to 0,0001;
- separate all meshgroups, assign cut numbers, clean weights, clone a new package.

But before you do that, clone any maxis item, export the blend and look at what the outliner looks like. Yours should look like that, too, not what it looks like now. There should be one rig with parented items. You have no rig in the scene at all.

Could uv_1 is the cause?

prnt.sc/26fyp43

I have tried to retransfer uv_1 from the reference a couple of times, but the result is always separated like that. All meshes were joined and doubles were removed when retransfered.

meanwhile the uv_1 of the reference at that area is all connected neatly.

To assign different properties to different parts of the mesh, you need to split it.
Interacting with other CAS items and objects, having a different shader, etc, are said properties.
If you want your item to function as intended by the game developers, you need to clone something that already functions the way you want. If you do not want it, you can clone something that is made of one meshgroup. This, however, will not always be possible, there may be problems like severe distortions in the foot area ( happens when foot bones are introduced to meshes where they were not present) or no transparency.
However, if you are keeping the mesh as one meshgroup for testing purposes, you can disregard these issues because you will be remaking the package anyway.

For example, in my tutorial above i say that, if you want your top to start hiding the shadow from necklaces, you need to clone something that already does it.
If you do not need this, clone a bra that is not tuned to hide anything because it does not clip into anything.
You need to choose items with as little sculpted details as possible to get uvs without rips. In your case, it can be a swimsuit joined with feet