Elligator map/inverse-map seems wrong

[hyggy2019]

Hi, there,
I've tested Elligator map/inverse-map with the code below. pk should be equal to pk2, however they often get different. Any help?

int Elligator_Test(){
std::cout << "Elligator_Test\n";
unsigned char pk[crypto_core_ristretto255_BYTES] = {};
unsigned char pk2[crypto_core_ristretto255_BYTES] = {};
unsigned char representative[crypto_core_ristretto255_BYTES] = {};
unsigned char* a = new unsigned char[crypto_core_ristretto255_SCALARBYTES];
bool success;
do {
crypto_core_ristretto255_scalar_random(a);
success = ScalarBaseMult2(pk, representative, a);
//ristretto_ropoGroup2Field(g_sum, buffs, mfe25519_one);
} while (!success);
std::cout << " pk = " << toBlock(pk) << " " << toBlock(pk + sizeof(block)) << "\n";
std::cout << " representative= " << toBlock(representative) << " " << toBlock(representative + sizeof(block)) << "\n";
std::cout << " a = " << toBlock(a) << " " << toBlock(a + sizeof(block)) << "\n";
RepresentativeToPublicKey2(pk2, representative);
std::cout << " After RepresentativeToPublicKey2, pk = " << toBlock(pk2) << " " << toBlock(pk2 + sizeof(block)) << "\n";
return 0;
}