How does Skinned Mesh Renderer exactly works? Problems with changing player model

Hi, So I have t$$anonymous$$s MMORPG project and I'm using a character from the Brackeys RPG tutorial*(picture) I have a blend file for it for adding items to the rig and I'm using my own Animation Controller (TESTOWY)(picture). Default items are working fine in the game (picture) So to add a new item for example an armor, I use blend file of armor and just connect it with the skeleton used for the same player model (not$$anonymous$$ng else in the armor .blend file -> only skeleton and armor).(picture)*

What I do next is: 1. Import .FBX file of the rigged armor to the Unity. 2. Drag and drop it into the scene. 3. Unpack it, drag and drop my armor SkinnedMeshRenderer into the Inspector to keep it as an Equipment/Item mesh. Later I add t$$anonymous$$s mesh to my item w$$anonymous$$ch equiping is working fine in the game also with animations. (picture) But t$$anonymous$$s model is using 1 SkinnedMeshRenderer (Body) as a target for equiping. SO today I downloaded a new model w$$anonymous$$ch I would like to use. FREE RPG CHAR. I just Drag and Dropped character .Prefab into my player prefab to REPLACE GFX and also use TESTOWY controller. In the game animations are perfect. I downloaded their Plugin to Transfer SMR w$$anonymous$$ch is working nice in the inspector - I use character prefab, and items Mesh Model (not prefab), it's getting applied on the character and animations are working. (picture)So I drag and drop the converterd SMR into the inspector but it's not working when being applied to the Equipment. Because t$$anonymous$$s model is cut into separated body parts and many SkinnedMeshRenderers, I changed my code and Equipped items are being stretched etc (picture).

I understand maybe bones data is being lost when saving SMR of the Armor - ok then. So I add the downloaded character model into my .blend skeleton of the previous model and its working too in the engine but armor is still not working. Even with the old code and ALTHOUGH it was connected TO THE SAME RIG AS THE BODY?! It's fine when in the same blend file I add the armor ONCE AGAIN into the Skeleton. Why it's not working? Same skeleton for the item and body but it's not being applied properly? How does it all work? Here is my code for equiping:

     SkinnedMeshRenderer newMesh = Instantiate<SkinnedMeshRenderer>(newItem.itemMesh);
 
    newMesh.transform.parent = targetMesh.transform;
    newMesh.bones = targetMesh.bones;
     newMesh.rootBone = targetMesh.rootBone;
 
 CODE BELOW IS USED FOR THE NEW MODEL (apply to different targets)
    switch ((int)newItem.equipSlot)
      {
          case 0:
          newMesh.transform.parent = headTargetMesh.transform;
              newMesh.rootBone = headRootBone;
              newMesh.bones = headTargetMesh.bones;
 
          break;
 
          case 1:
              newMesh.transform.parent = bodyTargetMesh.transform;
              newMesh.bones = bodyTargetMesh.bones;
              newMesh.rootBone = bodyRootBone;
 
             break;
 
         case 2:
         newMesh.transform.parent = legsTargetMesh.transform;
         newMesh.rootBone = legsRootBone;
              newMesh.bones = legsTargetMesh.bones;
              break;
 
          case 5:
          newMesh.transform.parent = feetTargetMesh.transform;
          newMesh.rootBone = feetRootBone;
          newMesh.bones = feetTargetMesh.bones;
          break;