When the body is deformed, outside of the clothes, and/or not aligned properly. If you have made a new project and started over and still have the same problems, it is likely an anti-rip tool some creators will put on an avatar. There isn't much you can do without the proper copy of the avatar. Some cases restarting your Unity Project, Unity Hub, and/or PC can fix some of the errors with misaligned body/parts. Make sure you're on the latest supported Unity and SDK.