As long as you can connect the id to one single client / user, it is PII. It does not matter, where this id comes from, a random hash, an encrypted IP adress. If it's unique, it's PII.
If you only save it on the server, not on the client side, it's not PII. But then it's almost useless for analytics. Because next time the user comes around, you create another hash and therefore another user.
