Are crypto-assets a challenge to tax compliance?

Could you elaborate on why some believe crypto-assets pose a challenge to tax compliance? Do they think it's due to the anonymity of transactions, the lack of clear regulations, or the complex nature of tracking and valuing these assets? How do these factors specifically hinder tax authorities from enforcing tax laws and ensuring fair taxation of crypto-asset holders? Additionally, what strategies or solutions have been proposed to address these challenges and improve tax compliance in the crypto-asset space?