I recently played with them using x10 multiplier i had over 600 losses in a row, and even after the first win appeared, the next line of losses was over 30 losses
600 consecutive loses in x10 is madness... it's like loosing 6 consecutive times on a chance of 99.9% to win. Was you friend playing with random high and low?
I would recommend to play always high or always low.
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I'm not that familiar with the technicalities of these server seeds or something similar kind of stuff but you're saying it should be automatically be changed on the player's side everytime for the next bet/s? If it's complex then for sure the alternative to do right now is just to change it on each bet.
What i mean is they have a dynamic Server Seed while a true Provably fair engine has an static and let the users change it when they want.