another variant (using GNU Awk 5.0.1) Handles standard ascii and dos formatted records

cat pablo.awk
{ gsub("\r",""); k[$1" "$2] = k[$1" "$2] + 1 }
END{
        for (ki in k)
                if ( k[ki] > 1 )
                        print ki
}

# running that produces
awk -f pablo.awk input
u   8574