Hmm, at some point, the game provides some Fortune Boxes.
Every account it is different, so we do not know in reality.
What we know, it is that around rank40 to 70 in that spot grinding for gold, the game provides the mix boxes or fortune boxes. Passing the Rank 70, then no more.
When I started to play, I got many fortune boxes but those were really good providing all kind of weapons torsos and modules. Some people get some and some people don't. I was lucky to get many but later on in 2V2 Hard or Insane overlord, it is very rare in my accounts to get fortune boxes farming. Soe players they get many farming and accumulate them on the hundreds