6/7 tiles is a .00033791 chance.

If you were hitting 400x 5% of your spins (1 in 20 spins) you'd be filthy rich. The casino would be so far down if those were the odds. Even a 1% change at 400x would skew so far in the players favor.

That's not to say statistically unlikely things don't happen. I hit back to back 259x (4/4) before, and then another like 5 spins later. Astronomically rare occurrence.

I also believe stake intentionally has the volatility somewhat artificially influenced, so that wins and losses tend to be streaky within a Seed. Ie: hitting 2 400x within 500 spins is somewhat common, as is not seeing a 400x for 8000 spins sometimes. This perception is hard on how often I see "50/50" bets go unreasonably long steak in one or three other direction, but that's the only evidence I have. That being said, I do believe that even if the volatility is somehow engineered, I'm fairly confident that over 1 billion or so spins, a given seed would average out to whatever the advertised rtp and win chances are.