Turnstile.register() will mint a NFT . When minting a NFT, the function does not check if a receiving contract implements onERC721Received().
_recipient can be contract address.
The intention behind this function is to check if the address receiving the NFT. If it is a contract, implements onERC721Received(). Thus, there is no check whether the receiving address supports ERC-721 tokens and position could be not transferrable in some cases.
Following shows that _mint is used instead of _safeMint:
Consider using _safeMint instead of _mint.
