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I created ERC20 compliant token on Ropsten testnet. I set in constructor that all of the token supply is added to my wallet address. When I open the metamaks I see that I have the tokens. Here's the screenshot[enter image description here

However, when I check the token page on ropsten etherscan here I see that the token holder amount is set to 0.

I saw this thread which shows somewhat similar problem except for the OP of that thread the etherscan properly detected number of token holders, it's just that the amount is incorrectly 0. The answers were that this is a temporary bug with ropsten etherscan but since almost 2 years have past I'm not sure if the problem that I encounter has anything to do with it.

Here's my contract code:

    /**
 *Submitted for verification at Etherscan.io on 2020-05-18
*/

pragma solidity >=0.4.0 <0.7.0;

// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
// https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
// ----------------------------------------------------------------------------
interface ERC20Interface {
    function totalSupply() external view returns (uint256);
    function balanceOf(address tokenOwner) external view returns (uint balance);
    function allowance(address tokenOwner, address spender) external view returns (uint remaining);
    function transfer(address to, uint tokens) external returns (bool success);
    function approve(address spender, uint tokens) external returns (bool success);
    function transferFrom(address from, address to, uint tokens) external returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

    contract AtariToken is ERC20Interface {

    string public constant name = "AtariToken";
    string public constant symbol = "ATAR";
    uint8 public constant decimals = 0;

    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
    event Transfer(address indexed from, address indexed to, uint tokens);
    event RegistrationSuccessful(uint256 nonce);
    event RegistrationFailed(uint256 nonce);

    mapping(address => uint256) balances;

    mapping(address => mapping (address => uint256)) allowed;

    uint256 totalSupply_ = 7777100000;

    mapping (string => address) addressTable;

    using SafeMath for uint256;

    constructor() public{
        balances[msg.sender] = totalSupply_;
    }

    function totalSupply() public override view returns (uint256) {
        return totalSupply_;
    }

    function balanceOf(address tokenOwner) public override view returns (uint) {
        return balances[tokenOwner];
    }

    function balanceOf(string memory tokenOwner) public view returns (uint) {
        address userAddress;
        userAddress = addressTable[tokenOwner];
        return balances[userAddress];
    }

    function transfer(address receiver, uint numTokens) public override returns (bool) {
        require(numTokens <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender].sub(numTokens);
        balances[receiver] = balances[receiver].add(numTokens);
        emit Transfer(msg.sender, receiver, numTokens);
        return true;
    }

    function transfer(string memory receiver, uint numTokens) public returns (bool) {
        address receiverAddress;
        receiverAddress = addressTable[receiver];
        require(numTokens <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender].sub(numTokens);
        balances[receiverAddress] = balances[receiverAddress].add(numTokens);
        emit Transfer(msg.sender, receiverAddress, numTokens);
        return true;
    }

    function approve(address delegate, uint numTokens) public override returns (bool) {
        allowed[msg.sender][delegate] = numTokens;
        emit Approval(msg.sender, delegate, numTokens);
        return true;
    }

    function approve(string memory delegate, uint numTokens) public returns (bool) {
        address delegateAddress;
        delegateAddress = addressTable[delegate];
        allowed[msg.sender][delegateAddress] = numTokens;
        emit Approval(msg.sender, delegateAddress, numTokens);
        return true;
    }

    function allowance(address owner, address delegate) public override view returns (uint) {
        return allowed[owner][delegate];
    }

    function allowance(string memory owner, string memory delegate) public view returns (uint) {
        address ownerAddress;
        ownerAddress = addressTable[owner];
        address delegateAddress;
        delegateAddress = addressTable[delegate];
        return allowed[ownerAddress][delegateAddress];
    }

     function transferFrom(address owner, address buyer, uint numTokens) public override returns (bool) {
        require(numTokens <= balances[owner]);    
        require(numTokens <= allowed[owner][msg.sender]);

        balances[owner] = balances[owner].sub(numTokens);
        allowed[owner][msg.sender] = allowed[owner][msg.sender].sub(numTokens);
        balances[buyer] = balances[buyer].add(numTokens);
        emit Transfer(owner, buyer, numTokens);
        return true;
    }

    function transferFrom(string memory owner, string memory buyer, uint numTokens) public returns (bool) {
        address ownerAddress;
        ownerAddress = addressTable[owner];
        address buyerAddress;
        buyerAddress = addressTable[buyer];

        require(numTokens <= balances[ownerAddress]);    
        require(numTokens <= allowed[ownerAddress][msg.sender]);

        balances[ownerAddress] = balances[ownerAddress].sub(numTokens);
        allowed[ownerAddress][msg.sender] = allowed[ownerAddress][msg.sender].sub(numTokens);
        balances[buyerAddress] = balances[buyerAddress].add(numTokens);
        emit Transfer(ownerAddress, buyerAddress, numTokens);
        return true;
    }

    function registerUser(string memory user, uint256 nonce) public returns (bool) {
        if (addressTable[user] == address(0)) {
            addressTable[user] = msg.sender;
            emit RegistrationSuccessful(nonce);
            return true;
        } else {
            emit RegistrationFailed(nonce);
            return false;
        }
    }
}

library SafeMath { 
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
      assert(b <= a);
      return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256) {
      uint256 c = a + b;
      assert(c >= a);
      return c;
    }
}
2

When you mint the tokens in the constructor, you don't emit a Transfer event.
So Etherscan doesn't know about the minting.

    constructor() public{
        balances[msg.sender] = totalSupply_;
    }

If you are creating ERC20 tokens you may want to look at the OpenZeppelin Contracts implementation to see if this meets your needs. See the documentation for details: https://docs.openzeppelin.com/contracts/3.x/erc20

If you have questions on using OpenZeppelin you can ask in the Community Forum: https://forum.openzeppelin.com/

Disclosure: I am the Community Manager at OpenZeppelin

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