In API.sp on the Native_RemoveClientFeature feature should be arg2, in git repo client and feature are both arg1
public int Native_RemoveClientFeature(Handle hPlugin, int iNumParams)
{
int iClient = GetNativeCell(1);
if (CheckValidClient(iClient))
{
char szFeature[64];
GetNativeString(1, SZF(szFeature));
...
}