When you meet someone for a second time, "It's nice to SEE you again" sounds more natural. Generally, we say "Nice to meet you" for the first time that we meet someone.

It's normal to say 'Nice to meet you' you for the first time, and 'Nice to see you' for subsequent meetings. 'Meet' in this sense means 'make your acquaintance' [fare la conoscenza] which - logically speaking - you can only do once. However, if you were to say 'Nice to meet you again' on the occasion of a second meeting, this wouldn't be seen as a mistake. You could interpret this as the other meaning of meet [ incontrarsi], which would be fine.

Both are correct, but "nice to see you again" is more informal. "Nice to meet you again" would be used more in a business environment or if it was a long time since you had originally met the person.

it sort of sounds awkward to me, I've never come across anyone who used such expression when meeting someone for the second time, and i agree with the answer above " Nice to see you again" is what would the typical native English speaker might say if he/she meets the same person for the second, even thought it's rarely used.