[Bugsy]

Try this

public ChatGlobalCommand(id)
{
    static lastsaid[512], said[512] , iPos;
    read_args(said, 512)
    
    if(equal(said, lastsaid))
        return PLUGIN_CONTINUE
    
    for ( new i = 0 ; i < sizeof BAD_WORDS ; i++ )
    {
        //The return value of containi() cannot be used as a bool since it returns -1 (true) if nothing is found. Always use != -1, > -1, or >= 0
        if ( ( iPos = containi( said , BAD_WORDS[i] ) ) > -1 )
        { 
            //Replaced replace_all() with setc() to fill in bad word chars with *
            setc( said[ iPos ] , strlen( BAD_WORDS[ i ] ) , '*' );
            //replace_all( said , charsmax( said ) , BAD_WORDS[i] , "***") 
        }
    }
    
    formatex(lastsaid, charsmax(lastsaid), "%s", said)
    client_cmd(id, "say %s", said)
    
    return PLUGIN_HANDLED
}