Without downloading anything, your UVs judging by the texture look ridiculous. I would guess this is not a bug and is in fact just insufficient margins around the islands on your UV. try making sure you’ve painted a little bit “outside of the lines” on your texture.
The way textures are sampled (especially at large distances) is imperfect and can catch edge pixels, this is a fact in any engine and you should always leave a margin.
This also happens when you zoom out from your player’s character. You can see that the edges of the limbs represent the tone of your avatar’s skin color rather than your ShirtTemplate or PantsTemplate. When zooming back in, everything seems normal.
However, setting the decal’s transparency to a negative value seemed to fix the issue for me, though now it looks weird.
This issue doesn’t seem to be a bug - it’s a problem that can occur when the UV islands on your mesh are too close to the outer bound of the texture area that is intended for the islands. When this happens, pixels from the texture area outside the bounds can leak onto the mesh and cause these strange lines to appear.
To prevent this issue from occurring, it is important to make sure that you allow a sufficient margin of pixels around your UV islands. This can be done by making sure that your UV islands are not scaled too close to the edges of the texture area intended for the islands. If you are doing a render bake of any kind, you can try increasing the margin value in your baking settings to help prevent these lines from appearing.
Technically not a bug, or at least a well known bug that’s been around since the dawn of time and will probably never be fixed.
Roblox loves to compress images to hell and back, so some bleeding in from the bordering pixels is going to happen to begin with, but Roblox also loves to bleed textures together when displaying them (this is especially visible on non square bodies wearing clothing that doesn’t go over the bordering outlines, as you can see them clearly appearing around the sides of the parts)
The only workaround is painting an extra pixel or two outwards from the islands so any bleeding that happens will be of the same colour, so you won’t notice it.
Like other people said this is not technically a bug.
The main difference is in how textures are sampled in a game engine vs Blender. All game engines use mipmapping both for performance and to reduce aliasing issues. Here is a good description of the issue: Edge padding - polycount
