I’m gonna cut straight to the chase, the 1.5.4b patch was supposed to solve the steam account authentication, but in return, some people had their accounts “wiped”, or so it would seem, in my case I have 2 email addresses, both of which have been used on the gaijin website, and which I can log in the game with, first one results in an empty account, but with 14k GS, Black Hort and Ghost, both of which I remember that I got via promo codes and coming from War Thunder respectively, but the second address does log me back in my main account, but then there is this:

So, bottom line, if you happen to be logged in an empty account, do not panic, your main account is not lost, it’s just that it may have been associated with another email address, possibly one that you linked that account with, contact support and ask them to associate it with another address, if you want to, after that, the issue with premium content should also be fixed.