Long sleeves glitch

Hi. Each meshgroup of the blend file you import in the package file must have the same exact vertex groups as the one that is being replaced. The mesh should also be split into meshgroups the same way the original is. This will insure meshgroups have no extra vertex groups.
You started a package from yfBody_DressMaxi_PatternRaspberry. If you export its blend file, open it and select s4studio_mesh_4, you will see that it has only 3 vertex groups. Meanwhile in your blend a mesgroup with the same cut number has all vertex groups of the whole dress.
You can deal with it in 2 ways.

The downside of this method is that if your sim will be wearing high boots, they might clip into your dress.
1). Select any of your meshgroups, Shift select the rest, Ctrl J to join them;
2). Download and install this addon;
3). Select your dress, remove unused vertex groups;
4). Clone this lingerie set, export its blend file, append it in the scene;

5). Select the appended lingerie set, in Object mode press G X and move it away from your dress;
6). Join appended mesh with your dress. Select the appended mesh in Edit mode and press Delete, choose Faces.
7). Edit your cut umber to 0000.
8). Save and import in the package started from the lingerie set
All meshgroups of maxis items have one random vertex group. No vertex has its values. It's just there and should be present in the list of vertex groups of your item. If it is not, there may be distortion like yours. If you won't get it in your game, someone else using your item will.
Since you are going to import your blend in the package started from a different item, you need to remove that extra vertex group it got from the old reference. Then you need to add the extra vertex group of the item you started a package from. You do not need to re-transfer the weights, combining two items will be enough. Then you need to remove this item.

The downright of the second way is that it will be a bit time consuming but high boots will not clip into it:
1). Delete rig.001, rig.002, rig.003, and bone_bone_shape.003 for your convenience.
2). Download and install this addon;
3). Select s4studio_mesh_1.000, remove unused vertex groups. Rename it to skirt. Rename other meshgroups to 01,02,03;
4). Clone yfBody_DressMaxi_PatternRaspberry, export its blend file, append it in the scene. Combine all meshgroups. Rename it to reference.
This item has skirt bones while your dress does not. To not edit forearm area again, re-transfer weight from the reference to the skirt meshgroup only. Select reference, Shift-select skirt, switch to Weight paint, choose Transfer weights, select By Name, use Clean tool with All groups selected. Now your skirt has all missing vertex groups. Delete reference;

5). Select 01, Shift-select 02 and 03, Ctrl J to join them, remove unused vertices. Then join them with the skirt;
6). Append yfBody_DressMaxi_PatternRaspberry again, this time without joining meshgroups. Rename each meshgroup of appended dress to their cut numbers;
7). Hide all appended meshgroups but 0000. Select your dress, disable Limit selection to visible, select the bottom faces so that they do not go above 0000 much ( it's best to not use Decimate modifier, reduce polycount manually ). Press P and choose Selection. Remove unused vertex groups, compare them to that of 0000 to see if you need to add or remove any, give it 0000 cut number.



Vertex paint dictates what variation (skin-tight and robe-like) of deformation map the painted area will deform according to in CAS during body customization and animation.
00FF00 is for skint-tight areas, 3FFF00 is for any skirt-like area ( skirts, bottom parts of dresses, coats, aprons, etc).


And the uvs in the uv_0 map are squished vertically.