So this is what I receive from Kraken,
I am an user to them, yet when I am hacked they don't help me to know how the hack was done. Terrible
I am surprised to see that an individual account is hacked even with 2 FA enabled and what is intriguing here in your case is that there is no other complaint about any other hacks, it is a really unfortunate situation and it looks like a targeted attack by someone you know, phishing and stealing your session cookie is the only way anyone could bypass the 2 FA restriction.