In AtlasUtilities:CopyTexture you use the Graphics.CopyTexture method.
This method, according to the Unity documentation, is very dependent on the type of compression, and therefore a number of problems arise when repacking the skin when the atlases are compressed.
https://docs.unity3d.com/ScriptReference/Graphics.CopyTexture.html

Graphics.CopyTexture can only copy memory with the same size (src=832 bytes dst=224 bytes), maybe the size (src=26 * 32 dst=7 * 8) or format (src=RGBA Compressed ETC2 UNorm dst=RGBA8 UNorm) are not compatible