I think only those with free account are affected. I have 2 accounts - 1 free & 1 paid. All my chats in the free account are gone, but I still have my chats in paid account.
I just had this issue with my paid account. I just canceled the renewal today, expiring in a few weeks, so I chalked it up to a clumsy downgrading system. Looks like not.
I just found out all my chats in my paid account had also gone.