Gas cost difference between first NFT mint and subsequent mints

Smart Contracts
1

Hey, I have a erc721 contract and I've noticed that the first mint uses less gas than subsequent mints and was wondering why that's the case. Is there a reason _safeMint would cost more gas the first time its invoke than subsequent invocations?

Here is the mint function fyi

function makeAnEpicNFT() public {
        require(paused == false, 'Minintg is paused.');
        require(totalSupply() < MAX_SUPPLY, 'Everything has been minted.');
        
        uint256 newItemId = _tokenIds.current();
        _safeMint(msg.sender, newItemId);

        _tokenIds.increment();
        emit NewSLNFTMinted(msg.sender, newItemId);
    }

Thanks

2

Generally I would expect the first mint to use more gas than subsequent mints. This is because changing a storage value from zero to non-zero costs more than non-zero to non-zero. See Dynamic Gas Costs - SSTORE.