What are the main problems with the following Tangle (IOTA), CryptoNote (Monero) architectures?

Question

Cryptography

Recently, I have become interested in a superficial study of the cryptographic mechanisms of various cryptocurrencies, and now it became interesting what are the main problems of the listed crypto protocols?
Of the advantages that I know:
Tangle: not a blockchain, but an acyclic directed graph, in which, instead of proof of work, confirmation of the previous ones occurs when new atomic transactions are added
CryptoNote: a blockchain, but not a classic one, but with ring signatures that allow you to hide the sender, recipient and transaction amount