Actually my worst doubling experince also happened at English Harbour(Oddson software). I was playing doubling in the 5$-10$ range (bet size could matter).
I lost like 23 or 24 out of 25 doubles and then I busted. However this small sample size says nothing. After this happened I stopped doubling (at all casinos).
I once made a test like you did at Playtech with a larger sample size and the
results showed a fair game. (Actually I had a little more wins than looses)
However my point is, where does it say that doubling has to be a fair game at online casinos?
Because at BEST you get a fair game, but there is no garantie. There are strict rules that
VP games/Dices has to be fair, but are there similar rules for doubling?
Zoozie